That kind of sucks, but since this games has guaranteed high sales a demo isn't really necessary. The Halo one wasn't needed either, but they were going for total media saturation leading up to the release.
Demos are like fittings room at a clothes store - you get to try on an outfit, and if you don't like it just put it back. I demoed Lost Planet and didn't like how the controls felt so it went from a "might buy" to a "won't buy." Conversely, I played the demo for Psychonauts on Steam, and am now planning on getting it form xbox originals.