Yes, there are many people who's rib cage is too small for their internal organs and therefore have a distended abdomen. No one is claiming that that's from GH or insulin. But pretty much every top bodybuilder since the early 1990s, pro and amateur have distended abdomens. You cannot find a single pic of a top bodybuilder, pro or amateur, with it prior to this. Something changed in the early 1990s that cause most all of them to develop the distended abdomen. It wasn't the amount of food they eat, it wasn't carbo loading. Bodybuilders have been doing that since the beginning. It wasn't the type or amount of steroids they did. They were doing massive amounts in the 1970s and 1980s. What did change was rHGH became widely available in the late 1980s and they started adding insulin to the mix in the 1990s.
Correlation is not causation, but sometimes it is the best explanation.
I said the same thing in a similar thread several weeks ago. The huge guts weren't there 15, 20, 30 years ago - and guys back then were no strangers to heavy training and eating, carb loading, cavalier roid usage (Pete Grymkowski and others), etc.
Also, the top guys 15 or more years ago tended to have a different look to their muscles compared to many of the guys today. The harder, denser (if smaller) muscle quality guys had back then was different (better IMO) than the "spongy" look many guys started showing onstage in the past decade or so. I believe the lack of the appearance of muscular hardness and density is also largely chemically related, although I guess some of it may be attributed to genetics, diet, and training.
Saying that the cause of these guts nowadays is mainly due to heavy eating and heavy training (and not primarily chemical) is similar IMO in a way to the magazines saying that better eating, training, and otc supplementation are the main reasons bodybuilders have gotten larger over time. Denial ain't just a river in Egypt.