San Francisco is starting to get away from this, particularly in the fringe / expansion areas of the CBD in the South of Market and Mid-Market areas.
There's actually always been residential space close to downtown, but it's generally been either tremendously expensive (Telegraph Hill), or near-tenement conditions (Chinatown). Parking is extremely limited and expensive, if you do own a car. There's also an issue with out-of-town HNVIs purchasing condos in or near the CBD but spending very little time there (other major cosmopolitan metro areas have similar issues, notably London).
Everything in SF is trivially nearby if you go by bicycle. I myself commute from Nob Hill near the Fairmont (Clay/Mason) to where Telegraph Avenue intersects with the UC Berkeley campus. I only take the Bart from Embarcadero to West Oakland. My commute averages 40-60 minutes and the variability is 100% how long I have to wait for the train (longer wait times in the evening).
If I had to commute within the 7x7 block that is SF, almost everything is within ~20 minutes of riding.
Union to Geary? A mile to Embarcadero, ~mile to Transamerica Tower? I agree these are trivial distances and agree with the parent that SF has mixed commercial/residential.
There's actually always been residential space close to downtown, but it's generally been either tremendously expensive (Telegraph Hill), or near-tenement conditions (Chinatown). Parking is extremely limited and expensive, if you do own a car. There's also an issue with out-of-town HNVIs purchasing condos in or near the CBD but spending very little time there (other major cosmopolitan metro areas have similar issues, notably London).