There is a big difference between the best QB to play the game, and the best passer to play the game. Rodgers may very well be the best "passer" to play the game thus far. He is on pace to be one of the best "QB's" ever, however saying that now is a bit premature.
Look at Rodger's mechanics. It is about as fundamental and sound as you are going to get. When was the last time you have seen Rodgers botch a snap? He prides himself on his ball security. He has a huge arm, and is deadly accurate, not to mention one of the best QBs at throwing the back shoulder fade, one of the hardest throws in all of football. Couple this with his mobility, I have seen him make so many free-running LB's miss that it makes me sick. The way he can manipulate the pocket, how he steps up, everything is spot on. Theisman is correct in this quote, there is no one in the NFL that has ever done it better. He is the total package at QB, end of story. Best pure passer in NFL history? I think so.