Aren't all the trailers by definition prerendered videos... or at the very least a pre-scripted scene running on the 3D engine with optomised views, options and selections.
Which in the end is still NOT representaive of in-game graphics and play, frame rate, shading and lighting - but rather an advanced show-piece of what the engine can do.
When you boot up your $60 game - you see nothing like the preview trailer..
