It's worth noting that San Francisco sets a much higher burden on new construction: it either charges the builder an "Affordable Housing Fee" (~$200k to $522k per unit), or it requires a certain percentage of units (12% of on-site or 20% of off-site) be made available for rental or sale at a price specified by the city ("below market rate").
Same issue in NYC. So a couple people win a lottery to get subsidized housing, and can't ever move again, at the expense of the people paying full rent, the developers, and everyone else who can't afford housing.
http://sf-moh.org/index.aspx?page=308