Think it's more a chicken and egg thing. Climbers tend to be very light and lean. I don't think it's necessarily a case that climbing makes them that way (but it sure doesn't harm it), but more their physique is suited to going uphill. High power/weight ratio. When we talk about pro's we talk about people who have adapted the phenotype pretty much as far as it will go. Their training is totally designed to make them as suited to their discipline as possible, but their physiology would have been somewhat geared towards that from the start anyway.

Having said that, the principles of adaptation to training are the same for all of us. It's just the pro's can recover better from high training loads.

An example I've used before, is that many pure timetrialists go to the mountains to train, very few pure climbers do motorpacing or time trial training. (One exception of Micheal Rassmussen after he f**ked up a time trial in the tour a few years back).