Some people would argue that the system determines the RB success more than talent. I've come to the belief that Buffalo is one of the premier teams in the NFL to own the RB for fantasy purposes. Just look how many carries Henry got when he was the starter versus how well he was performing at the time. Mcgahee's carries are at an insane level especially when you consider his ypc average hovers around 4 in most games.
Not too many teams in the NFL are willing and/or able to give their RB 30 touches week in and week out.