I agree that many in the persuits you mention do display impressive physiques. But at high level competition, you are dealing with people with exceptional genetics as a base line to work with. Naturaly close to pure mesomorphic body type, and a good adaption rate and potential that can be tapped through training.
Your theory also requires all athletes to have no regard for their appearance factored into their training. This is very often not the case, sometimes directly against the wishes of their coaches. A good friend of mine was Under 21 overall British powerlifting champion a couple of years back, and would 'sneak' to the gym i worked at to train his arms and shoulders against the orders of his coach!
To put it another way, some people who dedicate themselves purely to the training and eating required to increase muscle mass fail to make great increase in musculature due to being handicapped by their genetics, so to assume that performance related training guarantees a certain level of 'buffness' by default to everyone is a big stretch, though I do agree that a fit and active body will always have a better shape and appearance than an untrained body.
Just food for thought