Still much easier to get around SF w/o a car than LA (obviously with the caveat of LA being much larger and building their metro system at a rapid pace).
LA has a very good bus network within the city proper--one of the biggest in the world. It's possible to get within 1 mile of any publicly-accessible address by bus, and to neighboring cities (i.e., Santa Monica, Long Beach) and enveloped cities (i.e., Beverly Hills, Inglewood) as well.
LA's rail also enables car-free travel between Santa Monica, Culver City, Long Beach, North Hollywood, Hollywood, Pasadena, and Downtown. Including regional rail (i.e., the BART equivalent), it's possible to get as far out as Ventura County to the north, San Bernardino and Riverside to the east, and Disneyland/Orange County and San Diego County to the south.
Really depends where in the bay you are -- there are definitely areas outside of San Francisco you can do without a car. I lived in Berkeley and later Oakland without a car (probably four years total), and honestly it was pretty damn nice not having to deal with one. Menlo Park on the other hand? You'll probably need a car.
It's also surprisingly bikeable. Could there be more bike lanes? Of course. More are always coming at least. But when an artery is backed up (which it usually is), you can slither along the side, and with the grids there are usually residential routes that you can just fly along.
The city works if you are able-bodied without kids. In that case, you walk as far as 11 miles but usually just a few miles. It also sort of works for the people with $2,000,000 single-family homes, because driving to a distant supermarket (with parking) becomes an option.
Totally agreed that there's no place to park btw, yet another difficult thing about that city.
When I lived in the Sunset, I took the train, and that was worse than the bus - overcrowded trains meant that they sometimes skipped stops. So I usually biked instead.
The city is just not that big, most places are within walking distance if you're not going to/from far-flung areas of the city -- you can walk from the Marina to the Financial District in under an hour. (but the 30X made it a tolerable commute, usually under 30 minutes)
I'm just comparing the walkability to other major cities. I find SF to be pretty unwalkable all things considered. Especially compared to European cities or NY.