It really does. If you're getting 40FPS without 3D on, then with 3D on you'll be getting 20FPS.
As for Crysis getting "effectively 190% of the FPS in 3D", that doesn't even make sense, how can the performance go right up when you're turning a feature on that decreases performance?
it's to do with how the 3d is done, i'd guess the current method involves moving the camera every second frame, whereas the new method would be for every frame, take a second with the camera in a certain position