I think the commenter meant that while you can work at those companies in many places, if you want to be on the major projects and advance your career, you will have to be in the Bay Area. Google even has a fairly large office in SF, but usually people can't work on major projects there. You have to be at the HQ
As a happy resident in the San Francisco office, this is not quite true. To wit, there are major Cloud products in San Francisco, as well as Chrome, Android, and now a small VR presence. Also, Compute Engine started in, and mostly still remains fully based in, Seattle (the waterside Fremont office). Folks in the non-Mountain View offices may grumble about visibility, promotions, etc. but if you're just looking to work on something interesting in Google San Francisco (or Seattle, New York, etc.) they certainly exist.
