[mickt]

>If you're an employee you spend money where you live, not where you work

During the work day most of these people are 40 miles outside SF on self-sufficient campuses, often with free food. That means that during the week they're not in downtown SF supporting local cafes, coffee shops etc. But the same argument can be used for any commuter community, in this case it's reverse of many cities where people commute into a city.