Perhaps we're forgetting about the people who just use dSLR's as sophisticated point-and-shoots. The ones who buy the kit, photograph their kids, take them on vacations, and shoot birthday parties. Never comes out of AUTO or P, not very techie and so not likely to have any other lenses. I imagine this group makes up a substantial percentage of camera buyers.
Perhaps they notice digital noise but haven't really thought about all the factors that lead to digital noise. All they know is that if they buy a newer body, they will take cleaner images.
And that's all they want.