dvandom

It's not just a plot mechanism in movies, actually. I can recall at least one case where it's been used to give a role that's supposed to be homely (Moaning Myrtle, in Harry Potter and the Chamber of Secrets) to a Typical Hot Young Actress and then making her Glasses Ugly. Rather than, you know, casting a girl who isn't a hottie and thereby implying that those who aren't beautiful have a chance to break into films.