attraction?

Why is it that good looking nice guys are often going out with girls who are either not so pretty, quite bitchy, or a little stupid?
I met a guy last night who was all kinds of fabulous. Tall, handsome, intense black eyes, lovely voice, muscular, and a nice person. His grilfriend, while very friendly and pretty was not too bright. I guess I wonder how they would sustain the relationship, would the guy get bored and cheat? Or are guys happy with simple, uncomplicated women.
It reminds me of an episode of Sex and the City when Big is engaged to Natasha and Carrie asks why it wasn't her. He tell her that it just all got too complicated. When discussing this with her friends and making references to The Way We Were they realise that there are two types of girls, the complicated girls (with curly hair) and the simple girls (with straight hair). And guys will always choose the single girls.
Is this true?
Am I too complicated?
Would I have a boyfriend if I was simple?
Does this mean that my friends who have boyfriends are simple? I know that a lot of them are anything but simple!!