The guy doesn't leave the paint, he doesn't fight through screens, he won't show on a pick and roll, and he can (as it has been since 1996) be bullied in the low post. This fine post from Pickaxe and Roll leads to a series of other fine posts that echo what the proprietor of that site and other Nugget fans have been saying: Marcus gets blocks, and defensive rebounds, but he hurts his team defensively at times. I'm not going to go as far as to say that he hurts the team "nearly" as much defensively as he helps it - defensive boards and blocked shots still count - but Defensive Player of the Year? All-NBA Defense? No way.
Pickaxe noted back in June that Denver's defense was negligibly better with Camby on the floor and that "a truly great defender and shot blocker will alter many more shots than they block. Camby does not do that." Camby has always been a much better defensive rover than a shut-down post defender. And both KD and P&R's point is well taken -- the accumulation of defensive stats isn't a substitute for shot denial.