People talk about genetics being a copout, but this is exactly what people are really talking about when they say "genetics". The people that don't lift weights, don't necessarily diet and still weigh >200 ripped, what are they doing? If it ain't diet or training what is it?
Sorry for the rant, as to your specific q, I think it depends on the sport you're talking about. I think, given the appropriate predisposition, one could achieve the upper limits of "natural" physiology without "weight training". That said, you could quite easily draw the genetic 2-7 offsuit hand (sorry too much hold 'em last night) and end up needing all of the best diet and training to achieve equivalent muscularity. I think a lot of input will be anecdotal because it's hard to tell if the sport makes the muscle or if the muscle makes the sport, but for my $.02;
Rugby, LaCrosse, Gymnastics, and to a lesser extent Hockey, seem to contain/generate some of the largest non-lifters, IMO.