Google is not a San Francisco company. It has offices there, but no one can honestly claim that it is anything but a SV peninsula company. Nice list, but other than Dolby (and maybe, just maybe Twitter) these are all small companies whose significance in the long-term is quite questionable. Your list is about what one would see walking through any SV office park...
* iskoot * slideshare * rapleaf * wikia * ubisoft * google * gogrids * pivotallabs * technorati * dropbox * justin.tv * engineyard * heroku * socialcast * heyzap * yammer * sauce labs * shopittome * zenddesk * gigaom * twilio * bigtent * topsy * scribd * quantcast * cnet * lolapps * videoegg * snapfish * instructables * currenttv * vark * Sega * Dolby Research Labs * zipcar * kink.com
It feels rather hublike to me. That is just a small subset of the tech companies in my neighborhod that I happen to know about.