I think girls are much more emotions oriented, contrary to the boys who are more visuals.
That's why we can see for example Berlusconi or Sarkozy with beautiful girls. But you will never see Merkel with a male model

And we also can see this in casting. Pierre is not very good looking (sorry pierre), and yet, girls are often very horny and excited with him even before he touchs the girl.
On the other side, I don't know a lot of boy who would get horny with a woman version of Pierre.
That's why you shouldn't be ashamed of your looks when you're with a woman. BE A MALE and don't care about your looks because the girl don't care.
Simply : Men are visual, women are emotionals.
If you give the right emotions to the girl, you'll get her even if you're ugly.