Yeah, hard to understand how this is possible. But really, he's such an athletic specimen that he can afford not to use many of the tricks most defenders have to rely on to get the job done.
For example, he can wait for the ball to go up and then jump to block the ball, without having to risk contact with the person he's defending. He also doesn't have to rely on his hands to stop strong players from penetrating, etc.
So in all, it's easy to see when you come down to it why he doesn't get many fouls called on him. But even so... I think he's given the benefit of the doubt a bit too often.