I too agree about nudity and watching other people being nude is a primal curiosity. I'll admit that even though I'm adding a few years to the tally (I'm 37 this November) the primal urge of thinking about nudity and sex is an extremely prevalent activity. I cannot walk by a woman that I find attractive without wondering lots of things about her, one of them what she looks like without her clothes on. It's my opinion that most people's minds work this way, it's just that they don't like to admit it. To me it's the most natural of things.
Then comes the flip side of the coin, usually once the secrets are revealed, it's not really that interesting to fantasize about anymore. But the initial curiosity is what makes me click on the nude image links. Then after a while I study the beauty and grace of the human form, or the lack thereof - you know, things that make a photograph interesting beyond the initial wow. I find that very few nudes have real depth and meaning to them, or even beauty or good form.
It would be interesting to compare numbers of hits and numbers of sales. Is there any correlation there with nudity vs 'anything that lacks the presence of a nude human being'?