You do realize Ramon Sessions had a 20-20? Part of the reason Rondo has a high amount of assists is because he has really good teammates who can finish plays in KG, Shaq, Ray Allen and PP. The inflation effect isn't much, but it is there.
It helps to have really good teammates, but Rondo has clearly improved a lot as a player. He wasn't putting up these crazy stat lines two years ago with a lot of the same teammates.