>I "knew" when I bought corporate bonds paying 15% in 2008 that they would appreciate.
No, you're ignoring the case where they might have defaulted.
The housing market oftentimes works in cycles and changes with time. In my life I've watched the neighborhood I grew up in go from highly desirable to highly undesirable and now it's back to being desirable again. 30 year mortgage is enough time to see wild swings in technology, the economy, industry, and plenty else.
These all effect housing prices. Dramatically sometimes.
Mountain View is currently dependent on the tech industry and the flow of VC capital to maintain housing prices. Another .com crash and Mountain View house prices will crash accordingly. "Silicon Valley" may even move to the South or something in 20 years.
Right now the neighborhood I currently live in is in a boom due to a large employer here heavily ramping up production and the associated influx of people moving here from other parts of the country for work. I don't really expect the sort of growth we are experiencing now to last in the long term but who knows what will happen.
There's always the unknown.
A house is a house, enjoy it, but don't count on making money on it.