Hmm, I really like this explanation of Filch's attitude and behavior. The combination of pureblood wizarding pride (despite the fact that he's a squib and an outsider to nearly all of wizarding society) and pride in his own ability to be capable without magic makes for a very complex character. Snape, as a halfblood wizard (and one without a great deal of social intelligence) isn't equipped to understand this at all. Any sort of relationship between them was pretty much doomed to fail.