Huh. that's an interesting point I hadn't thought of; I always attributed the difference in quality to just, you know, the stricter housing code and better building tech in general... but that's not the only factor at work in Silicon Valley.

In Silicon Valley, sure, most of the housing stock was built rather a long time ago, yes, but it was also built to the expectations of people who didn't make a lot of money. The newer stuff around here is built for people who are in the top 5% or better of incomes, so it's likely they use more expensive construction techniques, too.