He defended Yao one on one in the playoffs, and he can post up. He's a 7-footer. He's a passable rebounder. I think he easily qualifies as a center. Novak -- not close.
Okur spends his time at the elbow extended beyond the three-point line, or low block. The former has been used by centers for years, even if they can't hit a three or won't even attempt a long shot. He might shoot threes, but he's a center. That's not even getting into the defensive side of things. Guys like Oberto and Robinson and Rasho/Nazr (to a lesser extent) hang on the baseline and high post, the domain of power forwards. Think about where Luis Scola was hanging out last season.
today's game is unique in that anybody 6-11 or over can play center. i'm sure we'll have landry play a lot at center next year, but i don't think anyone would confuse him as a center. okur plays center, but that's by default. the jazz technically plays 2 PFs and spread the floor, to open up the space for their shooters. if okur was on our team, he would be a PF. if he was on the warriors, he would be a C. that's why nobody confuses duncan as a C. you ask any basketball mind where duncan will go down in history as: it'll be PF. he's been called as the best PF UNANIMOUSLY by the media (except for you of course). the only pure center nowadays is yao, howard, erica dampier... guys that stay in the paint and do what a center is supposed to do.
It's interesting that you say "that's why nobody confuses Duncan as a C" as if you actually provided some logical reasoning. Why do you think Okur's style of play is consistent with that of a PF and not a center?