Let me say at the outset: I think Rick Warren is not a respectable human being. The fact that he has compared homosexuality to pedophilia and incest, and bars gays from entering his church, where he includes an “ex-gay” support group, suggests he is an immoral person. (He wouldn’t be the first evangelical to be immoral; in fact, are there any moral evangelical people?)
But I will say this: Obama is a moral person, he’s stuck pretty close to his word (with a few exceptions, >ahem!< FISA, federal matching campaign funds, >ahem!<), and he's extremely strategic in his thinking. I've said before that you shouldn't underestimate him, or judge him too early. I did so myself, and learned my lesson early on.
My guess? Obama’s going to make a big pro-gay announcement (either to repeal DADT, or, hopefully, give federal recognition to same-sex partnerships) soon afterwards, and he wants to make it very clear that he made a big, public concession to “the other side of the aisle” before he does that. The fact that the uproar among LGBTs and their supporters has warmed up evangelicals to their president-elect nemesis. That goodwill might be what he needs. He’s pissing off the Left now; hopefully he’s preparing to piss off the Right soon. Politics always involves pissing somebody off, right?
Let’s wait and see.