As a resident, seconded. Even living in San Francisco, the utility of a Caltrain connection is much reduced vs. BART. Was 10x too much to pay, if it is as the OP claimed? Maybe. As a former resident (and having grown up in) the east bay, the same applies: the Bart connection is much preferred to Caltrain, which is a big plus because the snarl of getting from the north-east bay to the airport is considerably worse vs. people taking their cars from the south bay, having also lived there as well.

I have also commuted on Caltrain, and liked it, but it's in weird places farther north, not well integrated with BART, and not frequent enough.

All in all, I don't think the difference in price (projections are awfully fickle) or at least utility is as clear as the OP suggests.