Put on your cynical hat for a moment (I have spares if you need one) and look at it from the point of view of someone hiring in SV. If employees aren't forced to live nearby, what happens to the million-dollar price tag on your house?

Now, if enough companies realize a competitive advantage from saving $100K/dev/year on salary and office space that a leak in the bubble becomes visible… well, it'll be fun to watch from a distance.