I think very few "natural born women" are built to their own specifications the way Allanah Starr or Carmen Cruz or Vicki Richter are. They're artificial, of course, result of plastic surgery, no doubt. But it's the same as with professional actors: They often are more convincing than the real thing. I'm not sure if that is still the case when it comes down to the nitty-gritty, but I've heard that real (and undoubtedly female) tit goddesses have a performance problem as well... I remember Chilli Palmer's "Lapdance 101" series in the good old BEhavior. No, I won't link it, find it yourself.