[tomkarlo]

You're assuming that a large share of those riders would take public transport, but most of them would probably drive, since that's what the large majority of people in SF who don't have access to a corporate bus do.

The bus provides an appealing (relative to the Caltrain) option that's appealing to people who could also easily afford to drive. (They're more convenient than the train or driving, to boot, whereas taking the train is much less convenient.) In doing so, they take tens of thousands of cars off the road each morning.