A ha! So that's why they're all live/work lofts:
"A zoning loophole exempts developers of such combined-use buildings from having to contribute to a city-run fund that subsidizes schools and affordable housing," according to Carlos Romero, the executive director of the Mission Housing Development Corp. (from an article in the WSJ about Andrew Beebe and bigstep.com, subscription required)
Sneaky developer bastards!