Isn't a demo supposed to convince you to buy the game? What's the point of a demo if you're only giving it to people who have already decided they're buying the game, and have fronted the money?
I mean, I understand the idea behind doing a preorder exclusive beta or something, because you want people who you know are buying the game, and are hardcore fans to enjoy the game you made, but a preorder exclusive demo is just a stupid idea.