It’s never struck me from interviews that Eric Kripke is really all that interested in the characters of Sam and Dean. I don’t mean to say he is disinterested but simply that it’s never been a focus of his. I gathered this from the DVD extras on S1 and it was pretty much confirmed from watching the Paley Festival session. For him SPN began as a case files type of story and the characters were literally an afterthought after his original idea was scrapped. I also gathered that it’s really Bob Singer, other writers and even Kim Manners who are more interested in the character exploration that most fic writers also latch onto, and who are largely responsible for fleshing out Sam and Dean. By comparison, for Joss Whedon the characters were everything and the story simply serviced our need to see the characters grow and and interact with one another.
I say this to explain why I think it’s impossible to determine from the outside what the intention actually was for Sam and Dean’s relationship because it seems to have been developed largely on the fly and with various hands at work on it. Certainly they were supposed to be both drawn together and yet antagonistic and I think that’s established pretty well in S1. But in watching “Asylum” (and “Skin”) in particular it seems to me that the relationship between the two was intended to be far more antagonistic than it was ever portrayed. While we can’t be too sure of the truth in what the shapeshifter tells Sam about how Dean resents him, as far as we can tell, Sam is being himself (if an enraged self) in Asylum when he tells Dean how much he hates him right back and is, in fact, willing to kill him. That’s a jump beyond annoyed, or resentful, the way anyone might feel about someone they’re in constantly close quarters with. At the end Sam tells Dean he didn’t mean it and it’s shrugged off, never to be spoken of again. My own sense was that Sam felt more guilty and alarmed at what he was capable of doing. This, after all, was a character who had never killed another person and who was as yet quite empathetic even with the spirits they hunted. You’d think that nearly killing anyone would have to truly shake him.
The other thing is that Dean doesn’t seem to be all that shocked that Sam might pull the trigger. He was, in fact, expecting it. By comparison I’d be pretty shocked if Buffy or Dawn ever did the same thing to one another, however resentful they can be at times. However it wasn’t all that shocking that Spike nearly killed Angel in Destiny, nor that he was willing to do so in S2 or in “In the Dark.” Although there is a détente bordering on friendship that develops in S5, and it becomes increasingly difficult to believe Spike when he tells Angel that he’ll never like him, I really don’t see so much of a difference in terms of what was written between Spike and Angel, and Dean and Sam. It’s especially difficult to know how things might have resolved themselves between the vampires because we never got a S6. In the post-apocalyptic world we were going to be given, it’s entirely possible that they would have drawn closer together, just as Sam and Dean did after John’s death.
At the heart of it I see the two pairs as having much the same bond. The differences come from their respective “family” environments. I’ve tended to see Spike and Angel not as brothers but as in-laws. However much Angelus shaped Spike, Spike was still a fully formed person before Angelus ever came along, with a history that had influenced him and continued to do so well into the future. By comparison, Dean had tremendous power over Sam. Even if Sam rebelled in his teens and began to see Dean in a very different way, a huge chunk of who Sam is is due to what Dean did or didn’t do with him and how Dean did or didn’t interact with their father. With both pairs I think there was both affection and betrayal. And there are also simply fundamental differences between Spike and Angel and Sam and Dean in how they see the world and one another that can be overcome, and differences in who they are as people that can’t.
I think that the whole reason Spike and Angel can become a team again in S5 is because they are the only two people in the verse who truly understand what the other goes through every day, and who understand how he got there. They aren’t much alike but have tremendous circumstances in common. Similarly, no one, not any other hunters we've met, could truly understand what Sam and Dean shared as children. Both pairs inhabit a world where everyone else they deal with are outsiders, and where they are borderline characters straddling two worlds. And I find it really interesting to see how much being mutual insiders can substitute for actual affection and liking. The power of mutual understanding, combined with a mutual mission in which they partner, would seem to me to be plenty enough reason for the characters to overcome the profound difficulties they have with one another and cooperate.
Another big difference in their histories though, is the issue of primacy. With Sam and Dean, it’s Dean – first born, in command of Sam for most of his life, and allied with the ultimate power for them, John. Dean, however, does not direct things – he follows. As I laid out in my earlier meta, he is Spike, not Angel. If we mapped this onto Spike and Angel’s relationship, Dru would have been the matriarch, with Spike following her loyally (and sometimes blindly), and Angel would have been the younger vamp, rebelling against his crazy and inexplicable parent, resentful of his older, frustrating sibling, and wanting to strike out on his own, following his own path (post-soul, maybe?). Certainly gives one a different view on how Spike and Dru might want to see Angel return to the fold in S2 (not to mention how cultured Angel seems to get out on his own with his artwork, designer-wear, and love of literature).
Of course, it didn’t actually happen that way. Instead Angelus came first, Dru came next, and Spike was last. And that picture makes me think of WIaWSNB. One thing I found curious about it is how the sibling order seemed to be reversed. Sam was the ambitious, achieving, mature (older) sibling whereas Dean was the going-nowhere-fast, scattered, (younger) screw-up who gets indulged by everyone. Obviously such stereotypes aren’t struck in stone, but they do tend to be true in a lot of families. In the real-world of the Winchesters, Dean isn’t the screw-up, Sam is. Dean is the “& Son” of the family business who puts his nose to the grindstone, learns things from the ground up, and is prepared to take over. He has no relationships because, for the most part, he can’t afford to and still do his job, but I could guess that if he ever did, she’d be a part of the business too. He told Cassie about it at the first opportunity. By Winchester standards, Sam is the pampered and protected sibling who feels himself misunderstood by everyone and goes off on his own to waste years of his life pursuing some selfish dream that will be of little use to anyone but Sam himself. (I should point out that Sam’s plans for law school tell us nothing about what sort of lawyer he would be. For all we know, he could have become a corporate tax attorney). The fact that he was planning to marry Jess but hadn’t told her anything about his family, seems to indicate he had no plans to have contact with them in the future. So in the “real world” all is as expected in the sibling order. In Dean’s alternate reality, the relationships are turned on their head.
And perhaps because of that we tend to assume that his estrangement with Sam is something wrong with the verse rather than the natural order of things. Because they were certainly plenty estranged in the pilot as well, and for the most part, Dean was trying hard and Sam was being indulgent (not unlike his indulgence in the Wishverse). What struck me though was how little Sam seemed to resent Dean in WIaWSNB compared to how much he resented him (at least on paper) in S1. And it made me think that this was a case of meta issues changing canon.
Aside from all the visual and spoken evidence indicating that JA and JP truly are the rare case in Hollywood, a pair of leads who not only get along but actually like one another, I would point to the screen as evidence as well. I have a feeling that the real-life relationship between the two bled onto the screen enough that even in cases where we were supposed the see seething resentment between two brothers, we saw little more than transient annoyance, exasperation, and verbal scuffles. To support that I’ll point to two different examples.
Even though Spike and Xander were supposed to be as antagonistic towards one another as Spike and Angel, I never found it as believable on screen. And this was explained in part when NB said that he disliked having scenes where he was forced to be awful to Spike because JM was his friend and it upset him to do it. (If anyone has a link to this, please point me to it. I believe it was said at a con post-series). Similarly at the recent Asylum con, JA talked about how it was relatively easy for him to be upset in scenes he would do with JP where Sam was hurt or suffering because he was looking at a person who was his friend and whose pain therefore upset him (I think this was part of his discussion about the end of “Heart” and the difficulty of doing dramatic scenes such as the end of CSPWDT). Granted, all these people are actors and professionals and will carry out scenes to the best of their ability regardless of its content. However, I don’t think it’s pushing it to say that the more the actors believe those scenes, the more believable they become on screen. And I think if you have people who actually get along well, then hostility and mutual dislike as opposed to disagreement are hard to get across convincingly. I also think that most actors want their characters to be likable and thus also try to make them less absolute and more ambivalent in negative scenes.
All of which is to say that I think fandom took the rosiest possible view on these pairs in most fic portrayals and that the shows (especially in SPN) minimized the deeper resentments between the characters as time went on. It intrigues me to think what SPN might have been like, had JA and JP not gotten along, but in fact, disliked one another. I would guess the continuing relationship between Sam and Dean would have been more actively resentful and distant, even while their partnership grew rather than more bickery and snarky as Spike and Angel were as they came together in S5.