Of course Asperger’s needs to be capitalized. It’s a name.
If it makes sense for that it makes sense for thread titles/contents, doesn’t it? I don’t see the logic in the question, I guess.
If I had to hazard a guess, or if I were the one in charge of discourse, I’d think the limits on comments would be to cut down on simple ‘lols’ or ‘I agree’ comments with nothing else in them, that sort of stuff. For threads, I’d guess it probably is primarily for spam, or so that you’re forced to be specific in describing your thread, rather than offhandedly just putting ‘MREs’ or something nonspecific.