Neil,
It's a similar situation around here. Most homes have been built 1 story, with the older stuff 2 story. I've noticed though, that the upscale stuff is starting to go back to 2 story, or 1 story with finished, walk out basements that look like the main floor.
A lot of ours came from the oil crunch in the 70's. Everybody started building smaller houses. Now energy is cheap and insulation plentiful and the houses are getting bigger again.
I assume the slab floors there are due to easier cooling? We see a few slabs here, but they haven't been real popular because the floors are too cold in winter. They're just starting to make a come back with radiant floor heating.