There are many erogenous zones on the human body, and they're not sexualized like the breast is.

As for the idea that women are different from men and have sex for different reasons than men, that comes from scientific research on the brain. I'm not saying I agree with it completely--I've had sex without feeling the "bonding" and "attachment" they're always talking about, and I know many other women who say they also have. Society does, however, make it out that women don't want sex, especially teen girls, or at least aren't as horny as men, but I disagree. Dr. Laura Berman was a guest on The Tyra Banks Show not long ago, and she pointed out something that actually makes a lot of sense. Since girls are often taught (more than boys) that masturbation is bad and shameful, girls sometimes don't learn how their bodies work and how to pleasure themselves, so their first experiences of these wonderful sensations come from boys, kissing them and touching them, so they might think only guys can give these sensations, and thus have sex more carelessly and unprotected.

I think girls are taught that they need boys, and that they're worthless without a boyfriend, and perhaps fairy tales add to that idea (the princess being rescued by the knight in shining armor), so they tend to romanticize what guys want and are like, and have unrealistic expectancies when they get in a relationship, and often feel that sex will cement the relationship.

That said, I think some girls and women have sex because they want sex, and I don't think there's anything wrong with that.