IME this is definitely true and it's often very intentional. One of the major reasons SF stole the startup scene from SV is that younger startup employees wanted to live in SF. As a startup founder you are very strongly incentivized to go where the talent is (or wants to be). When I was considering where to set up my startup a few months ago this was a huge consideration. Not quite at the level of HQ, but there's a reason Google has offices in both SF and South Bay as well, or in both SLU/SLU-area Seattle + across Lake Washington.
> If more people are like me who prefers living outside of the city proper, then I'd imagine a company will have access to more talent by moving its headquarters to the south of SF. I don't think it's about more vs less as much as matching the demographics of your typical employee. Eg experience levels, pay, work culture, personality, mix of job roles