I think, for men at least, the digital babe in some ways allows the artist and the viewer to more easily escape into the fantasy (perhaps erotic) than does a photo of an actual living hottie. I also think that part of what makes the digital babe pin-ups attractive is exactly because they can break the boundaries of nature. For instance, compare the digital Lara Croft to the Angelina Jolie version. I'd bet that some folks prefer the digital version over the living version. BTW, I'm hopelessly hetero, yet I like making hunky male pin-ups. I think it's because they represent what I'd like to look like :P