To try and separate out the various reasons why we are drawn to nudes into logical categories, as if we could somehow quantify and logically analyze it is a fool's task. There is an instinctual component, a sexual component, an emotional component and an aesthetic component. All of them swirl together in an ever-changing stew that has a different recipe for each person. That stew is what makes sure that the qualitative response in you is different than that in me than that in Heather.
I have to agree with Scott on this one. I shoot pretty much nothing but female nudes these days and don't try to explain why other than it's a serious passion for me.