Okay, MazingerDUDE officially became Chandoo's favorite pixel counter
Of course, the 2D mode is being rendered at 1280 x 720 res with MLAA.
Even the alpha channel is cut half (alpha in the 2D mode of KZ3 is quater of the 720P res (640 x 360) as KZ2) creating some horrible aliasing artifacts.
I see a lot more pop ups on 3D as well. (even with the halved res, you'd still need to render twice the geometry with 3D)
Here's a pair of comparison shots between 3D & 2D.
I'd personally take 2D over 3D any day, especially with what the current generation of 3D TV has to offer.
Don't say I didn't warn you lot about 3D
Killzone 3 SCEA producer interview: