Gears of War didn't have a demo for you all to pore over, and it went on to do OK for itself. So there's really no need to go changing things for the sequel, with Epic announcing that they've no plans to release a demo for the upcoming shooter. Epic's Tanya Jessen told Shacknews:
[There are]no plans for a demo. The reason being that it's been such a fast turnaround. A two year production cycle, for a game of this calibre, is really short.
Look, they're in a hurry, so just trust them, OK?
No Gears of War 2 Demo Planned [Shacknews]