I think it's just an extension of the hate people have for Emma Watson. I don't mind that her hair isn't oh-so-bushy like in the books, partially because it could be what you mentioned, and also because I refuse to believe that Hermione isn't smart enough to invest whatever the wizarding world's version is of anti-frizz conditioner. Even if she doesn't care about looking perfect, from a practicality/OCD standpoint, I find having little frizzes of hair popping out of my pony tail really annoying.