Over or Under Standing

It's been hard to miss the brouhaha over San Francisco's same-sex marriages, especially now that various conservative groups are suing to annul the marriages and to enjoin the city from issuing any more same-sex marriage licenses.

My question is this: how is it that anyone has standing to sue the city? I can't see any legally-cognizable injury that these groups have suffered as a result of the marriages. Their "interest" is presumably that California law be properly enforced. But -- at least in federal court -- the interest that all citizens share in having law properly enforced won't even get you in the door. That sort of thing is supposed to be the province of the other branches of government. No one, for example, can sue the IRS for failing properly to enforce the tax laws against particular taxpayers.

From this, I conclude that federal standing law and state standing law must be two very different critters. But it's not like I know this, nor like any of the friends I've asked knows. Just another thing they don't teach us here at the University of You Suck Law School, where the only thing that matters is federal law and the actions of the federal courts.