I disagree.
Playing a sport makes it a **** load harder. You think trying to add muscle on a cut (near impossible) is going to be easier on purely diet or sport and diet? If you play a sport you're gonna kill your recovery and make it so much harder to maintain/build muscle.
Yes, you can eat more if you do more sport but the stress of playing a sport is a lot more than cutting down on some carbs.
I think it's wrong to say most who play a sport are very lean. Most who are very lean are just lifters/bodybuilders. Yes you get some 100m runners who are very lean but don't forget they are all on drugs. Plus, yes, they're quite a few lean/big NFL players but again most are not HYOOGE or very lean.
Edit: And let's not forget that most of these guys at the top of sports are genetic gods! Thus they will have it all - strength, size, lean - which will rarely be the case. Think about that one. Genetics matter a **** load too - who can boast a 315 bench press at 14 years old? Kirk Karwoski can, I doubt many could.