You can say the exact same thing for Gears of War scene they shown. "Xenon" (as in devkit, not the final hardware) of course couldn't run it as fast because one X800 doesn't have a chance against 2 SLI'ed 6800s. How much does that say about final hardwares, I don't even care to speculate.
20FPS would be genereous, as he said. 15FPS is more like it, and it was like that even during the scene where not much happened. However, it's the dev kit. Not the final hardware, so noone should be getting their pants in the bunch.