I feel like sometimes that's done as a form of censorship, though...like maybe you have this little girl in an action comic, and she wears a dress...do you really want to flash her panties all the time just because it's more 'realistic'?
I guess if you're doing a comic with an art style that's heavy on realism, that's a dilemma you have to sort through...but in comics with cartoon styles, I think it can be forgiven if clothes don't always move the way they should. Heck, if the movement of clothes and hair looks better 'artistically' than it would 'realistically', I'll always pick artistic. Life's too short~