right, food does not make your internal organs grow. however, talk to any of the guys at the national level and above, and they will tell you that the majority of distention comes from overeating.
when you consume large amounts of calories (6500-7500 per day) your stomach and associated abdominal muscles eventually begin to relax to accomodate the large amounts of food taken in. this is exacerbated by lying down after eating. ever look at a male silverback gorilla?
most of these guys are eating enormous amounts of food in the off season in order to gain weight, because as we have all seen mass rules the game right now. you wanna get big, you gotta eat. period.
you also have to take into account that the walls of muscle in these guy's abdomens become very, VERY thick over time with the heavy squats and deadlifting and general stress that the abs (and lower back really) go through during heavy lifting.
do steroids and growth hormone cause internal organs to grow? absolutely. there is no doubt that in an anabolic phase other tissues in the body grow besides just muscle.
however you cannot say that the distended bellies of the top mass monsters are due solely to the use of hgh. if is more likely due to the all out pursuit of mass (extreme amounts of food and drugs and heavy lifting) that is required to get to the top of the game.