actually, it's probably true that the average Bodybuilder type is larger than the average joe, just not by the massive proportions claimed here. the guys that are drawn to (and excel at ) bodybuilding tend to be high-testosterone neaderthals even b4 juice, and that usually equates generally speaking to larger shweens.
as to your percentage, over 7 inches would be in the top 93%. over 6 i think is just in the low-mid 80's somewhere.