I guess generalization in anything causes a certain effect.
For example, if you say 'Well, they're beautiful, so obviously they can get whatever they want without making any concessions, and they don't understand give-and-take'...
These people in the general categorization will pick up on it and are pressured to act in a better way.... I think? Make sense?
Is it just the case that if you're beautiful, you've got less to worry about in life, and you build up a stronger personality that way?
Depends on how they were brought up, but if you're beautiful, you generally will have eyes on you, people watch your actions more often than those who are not visibly beautiful. So these people, knowing that eyes are on them, are pressured to put a lot of effort and energy into acting in the right manner.
I don't really know, just my thoughts on it...