Are you forgetting the advancements in supplements? The advancements in science that help us develop better nutrition plans? Hell even the advancements of training machines?
name any training method (HIT, etc), any diet (cyclical ketogenic, carbo loading, high fat, low fat, etc), and someone was doing it in the 50s and 60s. they didn't use those names, but you can find articles in the mags describing it.
Nor do I see how any machine would allow a natural bodybuilder to counter the effects of time.
So I guess natural bodybuilders can accomplish so much more than they could 30-40 years ago because of Designer Whey, Anabolic Xtreme Rampage, and NOExplode.
Really the only thing that might be affecting today's natural bodybuilders is the massive amounts of caffeine they are consuming in these energy drinks. But then are they really natural? Large doses of caffeine is banned in the Olympics.