This pretty much seems reasonable. Housing demand should probably depend mostly on the amount of wealth (maybe this should be income?) in the area. It seems possible that wealth in the valley is growing at 20%.
20% growth would mean the wealth in the area would double every 3.46 years.
This morning, it was announced that the US GDP grew at an annual rate of 2.9% last quarter, accompanied by the WSJ headline "US Economy Roars Back" [1].
Inflation in the Bay Area is around 20% YoY, based on price increases in the housing market.