Vince probably thinks that by giving us matches with no rules on ECW, it will make things like Street Fights and No-DQ matches on Raw and Smackdown seem less special, and not as worthy of their stipulation because you can get that kind of stuff for a solid hour on ECW. Also, he's scared of people getting injured and wants the new ECW to be a place where he can send talents that he thinks need to develop a bit more; like a higher level OVW/DSW - so putting them in no-rules matches with nothing but highspots would be unlikely to develop their wrestling talent. He probably also has a warped feeling that if he gives every match the no rules stipulation, then it'll get old, and like I said before, make them seem less special.
I think a good thing for him to do would be to make title matches no rules matches - so that we don't see any more of the bs finishes like the one at the Rumble. But I guess he probably won't do that because it's not his way of doing things.