"With Randolph you have a really thin player, and an inconsistent player. But he has insane athletic ability and some innate talent."
With Randolph's many talents, why would you tell this "really thin" player that loved showing off his athleticism and creativity to go bang the boards to the exclusion of everything else. If you factor in the increased minutes per game that Randolph played in his second year over his first, it seems he actually got slightly less rebounds per minute in year 2 over year 1. (22.7 minutes and 6.5 rebounds in year 2, 19.6 minutes overall and 6 rebounds a game for his career.
Beidrins at center got 7.8 rebounds in 23 minutes, and Gadzuric also a center only averaged 2.9 rebounds in 9.8 minutes. Also their power forward, Brandan Wright averaging 17.6 minutes a game only averaged 4 rebounds a game. So the 2009 Warriors definitely had a team weakness at rebounding and desperately needed someone to fix that problem. Clearly that's why Golden's State was so aggressive in going after David Lee who definitely knows how to grab more boards.
Nelson seems to have been telling Randolph to sacrifice developing the rest of his game, to try and fix a weakness of the team. Because Randolph had so many other talents, why wouldn't Nelson want Randolph to develop those other talents thereby increasing his value to the team over time? Does anyone think that telling Randolph to concentrate strictly on rebounding was a valid idea for a talented developing player? Making him do what he wasn't good at, and denying his ability to do what he was good at, seems a recipe for causing Anthony Randolph to rebel, which apparently is what he did.