This is something I've always wondered. It seems like guys at higher bodyweights can just get away with eating less cleanly, yet still preferentially add muscle rather than fat. I suppose if your maintenance is 4000kcal, a large pizza really won't set you back that far, versus someone with say a 2000kcal maintenance level.
So I guess my question is: does some critical threshold of muscle mass to height exist where the body is simply able to send the calories "where they need to go?" As in, is there some physiological change that happens at some point where the body can just handle excess calories in a better manner? It seems like there's sticking point of around 10 - 12% body fat for guys who are merely "normal" sized, where the huge guys seem to be able to lean out more easily while still retaining significant muscle mass. Yet when they bulk, they seem to get less sloppy. Hanging around this site, it seems like bigger really is better - the more lean muscle mass you have to work with, the better of you'll be in the long run.
Aside from "genetics" being the simple answer, larger frames can also carry more body fat and not look "fat". 18% body fat on someone who only weighs 140lbs would make them look completely out of shape. That is because they have very little muscle mass on their frames, assuming they are of average height. Someone who weighs in over 260lbs at 18% would simply look like they weren't that defined. They would still look huge and "built". This is one reason why your actual body fat percentage means a hell of a lot LESS than how much lean tissue is under it.
I don't eat pure crap when gaining, but I sure as hell don't avoid some food items that seem to send some of the people here into fits and convulsions. It simply isn't everyday or every meal. Along with all of that, the more overall body mass you carry, the more you can get away with in terms of food choices. If it takes 5-6,000cals a day for a larger guy to even gain weight, it isn't like that one hamburger with no mayo is going to set you back unless you are simply overly paranoid about gaining any body fat when gaining muscle.