To the first sentence: I don't think the theme is "class", though. It's your behaviour matching your class. To continue the comparison between Parker and Scrooge: Scrooge's behaviour didn't match his station as a wealthy businessman, so something happened to him to show him how wrong he was and so he would mend his ways before it was too late. Parker's behaviour also didn't match his station (as a superpowered being), so something happened to him to show him how wrong he was and so he would mend his ways before it was too late.
The only difference was that Scrooge got a warning, where Peter was giving an object example of the results of his meanness.
To the second: Certainly. But it seems like the argument is going too far in the opposite direction, that there aren't class issues in superheroes. The thread originator's argument that they aren't there because a lot of them were poor misses the fact that superpowers can be seen as a metaphor for class, so actually economic background doesn't matter as much. It would be like arguing that the X-Men aren't about being a minority because they all come from different ethnicities, some of them not minorities.