I don't buy that for a second, mainly because the Spurs aren't dumb enough to take Wemby out of the paint on defense just so he can stay close to a 30% shooter from the arc. The Spurs simply didn't rotate to Clingan, they left him open. If he'd made more, they would have simply rotated to him with perimeter defenders rather than taking the DPOY out of defensive position
this was a case of Portland parking the best offensive rebounder in the league 25' from the rim with the misguided belief that was a smart way to minimize Wemby's defensive impact. The Spurs were never going to cooperate with that nonsense.