Your question was answered; it has nothing to do with the case where you're "generating thousands of frames and throwing them away". What you want is a rendering engine that will perform at 60fps in the worst case. What engine devs want to write is an engine that can do better (even much much better) than 60fps in the average case, and be allowed to slip in those pathological cases. Gamers want more frames. More frames than is noticeable. They want some slack so that if something totally unrelated to the game ties up the machine, the framerate drop is not noticeable. They want to be able to double it so that they can drive a 3D display but still have the same effective framerate per eye.

Having a consistent 40fps is much worse (for a gamer) than a variable framerate that will dip down to 40fps for 1% (or 10%) of the play time. Having to limit your most complex scene to what can be guaranteed rendered at 60fps is much less appealing to a developer than making sure all the likely scenes can render at 60fps.