I think they are.

I've worked here in SF as a Rails consultant for the past four years. It's quite obvious that the work force skews younger. My best friend just became a CTO and his bosses are both 20. He's 41. :-0

When you look to start a family, the pressures of working in the valley are going to bubble to the surface. You can either endure a 60 minute drive (that should really only be 20 based on distance) to a child's dr. appt for which you endure wall-to-wall traffic with a screaming child, you try to ride bart with a child in stroller and packed cars, or you shuttle a car seat to and from an Uber.

Or, you pay 30-60K for a nanny and let them handle those headaches.

It's hard to live in SF with a family. Really hard.