Timmy has also constantly had a superior team to Dirk his entire career. That helps a lot.
Like I said... give Dirk 2 guys who are legit all-stars, like Ginobili and Parker, along with a cast of players that can step up and hit shots when called upon... Dirk would have been winning les too. He took a team loaded with inconsistent role players, put them on his back, and carried them to the Finals, making big play after big play on the road, constantly stepping up when the opponent seemed to have control (game 3 vs. Memphis, game 7 vs. Spurs, game 5 vs. Suns). He played better than people gave him credit for against the Heat as well, and made quite a few big plays. Unfortunately, Wade was just a little ahead of Dirk there.
Then again, you are a Spurs fan, I'm a Mavs fan, so we are both going to be a little more biased for our own player. But I don't see a whole lot of proof showing me that Duncan has been any better of a player than Dirk has over the past several years.