Plus many folks in sf don't have cars, prefer not to drive, and want to avoid paying $1k/mo for a car (parking in mission is often $350/mo; insurance at $60; gas + note).
Yes: this is one key point, avoiding car ownership (and making do with zipcar et al for weekend trips) is pretty much the only way to make SF affordable.
(Background: I'm deep in South Bay, but that's taste and preference not an absolute view I want to impose on others).
