Twin studies beg to differ on that point mate. Genetics does play a major role in what path you will follow in life, and I did not say you would be automatically good at a sport, many people tend to gravitate towards areas of their life that they are good at, be it sport or academically.
People seem to be talking about strength a lot. A trials bike doesn't weigh a lot. The only awesome tank of a rider I've seen is Dani Comas and he appeared to tank up after being out injured for a year or two. Some of the riders like CLS, and Tunnicliffe look dangerously skinny, it looks like they are doing a bit of cross-training for high jump. You could probably put a 15yo football player in the gym and he could out squat and bench them, but who could sidehop higher.
You guys watched Federer in the semi's, amazing power, and racket speed, technique, placement etc.... He could not lift much at the gym. I could guarantee that, I could assure you that if tanking up would help the power of his serve/shots, he would have done it.