i have no doubt some of the athletes in the bigger countries are on gear of some sort, but regardless gymnast have amazing physiques.
there was a young boy around 14 at my old gym ( my gym was on a higher floor that looked down on the gymnastics hall.) he was a scottish champion gymnast, he never lifted a weight in his life yet had pecs, abs, lats, arms, back, legs and ripped to the bone - complete development. he was not on gear, so some of these guys could also be natural.