Sorry to be blunt, but that's how "supply and demand" is really supposed to work. If Seattle supplies the same quality of housing for half the cost of San Francisco, buyers/renters should flock to Seattle, thereby reducing demand in SF and eventually causing SF housing prices to come down until the market finds an equilibrium. Trying to lobby for "below-market-price" housing is always going to be a losing game; the only long-term solution is to make the market price lower.
Unfortunately, competition among cities to attract residents is not like competition in other industries. A lot of people are stuck in a relatively small geographical area their whole lives due to employment, their children's education, various kinds of emotional attachment, and the sheer difficulty of uprooting themselves from a familiar neighborhood. This creates a captive market, severely limiting the effectiveness of inter-city competition. And of course, whenever there's a captive market, there's somebody who profits from it. In the case of SF's housing market, entrenched neighborhood groups and "below-market-price" renters enjoy benefits at the expense of newcomers to the city. Perhaps they actually deserve those benefits. Still, it's unfair to everyone else.
But there's one group of people who can afford not to be bound by the usual excuses that keep people stuck in a captive market. That's us, the techies. We don't need to be in any particular city in order to write code. Most of us are young and don't have kids. Few of us have any "root" in the Bay Area, so we couldn't care less about being uprooted [1]. There is no reason for us to be a part of San Fran's captive housing market. We can pack up and leave, all 8% of us if possible. That would be "supply and demand" doing its work.
Of course, there are a few problems with this proposal, including the fact that there really is such a thing as social networking of the offline kind. The Bay Area undoubtedly has one of the best tech "scenes" in the world. But I see it as a problem that needs to be fixed, not merely an advantage that we're free to exploit. HN, for example, requires everyone to move to the Bay Area, perhaps for a good reason. But in doing so, they directly contribute to, and exacerbate, the hideous distortion of the Bay Area's housing market. It's like mandating that everyone meet at a particular Starbucks. It makes sense when everyone you want to meet is already a regular of that Starbucks, but when the manager of Starbucks begins to take advantage of its captive clientele, you should seriously start considering an alternative.
Remember, the only vote that the market respects is a vote with your feet, i.e. a realistic threat to do business with a competitor.
[1] Disclaimer: I've lived in at least seven different cities in three continents, and harbor no particular emotional attachment to any of them. Apparently I'm incapable of developing an emotional attachment to geographical coordinates. But I must confess that I kinda like it that way.