This is only true if you strictly mean the city of SF, i.e., the tiny metro at the very tip of the peninsula. If you mean the metropolitan metro area, than SF is a nightmare without a car.
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.