The average travel times by BART don't seem all that bad, most large metropolitan cities need an hour by transit anyways. Do people in SF-region really not commute to work from afar?
Anecdotally, half the office (in a small startup) I worked with drove to a BART station, then took BART the rest of the way.
Also, I'd say the sprawl goes pretty far. I grew up in Vacaville, and it was not uncommon to commute into San Francisco. That was 50-something miles away.