When I show pictures of my house to my students, they think my family is rich. Of course we're not, though we're fairly well off, but Japan is more like England in this case than otherwise. If anything, living spaces are even smaller here.

There's another factor, of course, that being length of history for the general population. In both Japan and England, people have been building and rebuilding in the same locations for more than two thousand years. In the US, it's been about three hundred years for the oldest locations (yes, I'm discounting the native populations, because other than out west, they didn't build very permanently). I can't help but think that this has an influence on how much space people expect to have.