There is just too much temptation and drugs that can help them that will clear the system super fast. I won't believe for a second these guys have NEVER touched Test susp or TNE, and possibly tren. I also don't believe these guys that are in their 20s with these physiques naturally. Perhaps by the age of 30 something, MAYBE some of them are attainable, but we're talking about guys with less than 10 years of lifting in some cases.
Lastly, as already mentioned, there are a few natty guys who think cutting should be done naturally too. THere was an entire youtube battle going on between icecream and 3DM over this one. Icecream saying "There is no way these guys are natty when they "grow in to their comp condition". They should be losing muscle, but somehow they are gaining muscle! I have to agree with him here.
Not going to throw names around here, but I am friends with a former top level natural BBer, and he actually came to me for tren, because that's what all the guys were doing and he couldn't get his hands on any. He had been using deca for years before that and had to stop that in order to keep competing.