I know the conventional wisdom re: muscular hypertrophy is that moderate (8-12) reps with moderate to heavy weight is generally recommended for maximal muscular growth. Similarly, low resistance, high repetition work is usually looked at as being good for muscular endurance and cardiovascular fitness yet, terrible for building mass.
However, there seem to be some obvious exceptions to this. Distance cyclists often have massive thighs and calves. The so-called "prison workouts" which typically centre on extremely high reps of standard bodyweight exercises often seem to produce well-developed upper-bodies (Herschel Walker and young Mike Tyson are examples). I believe Chad Waterbury wrote an article on here in 2001 (?) regarding a self-experiment he did where he performed literally thousands upon thousands of chins and pull-ups over several months and noticed substantial back hypertrophy. German Volume Training also seems to fit this description although the weights used, while far from maximal, are still more significant than bodyweight or the resistance of a bike pedal. I'm sure there are other examples that I've missed.
Therefore, my question centres around how this can be explained. Is the conventional wisdom generally right until it's pushed well beyond typical limits (ie. doing 50 pushups wouldn't cause much growth but doing 1000 will)? Is it that this extreme training volume elicits substantial growth of the slow-twitch fibres to increase mass? Or are these examples simply genetic freaks that would respond with muscle growth no matter what training methods were used? (Keep in mind that I'm not saying any of these examples are pro-bodybuilder level physiques, just that they are much more overdeveloped than you would expect from such training).