They played as his back up band for a show, and he's been quite vocal about how much he likes them, so it's not too surprising that they'd send him something before officially releasing it. Plus, letting Kanye "leak" it through his blog gives them more exposure than giving it to their label or one of the normal music sites. Makes sense to me. I agree that Kanye is awesome (musically, personally he's a douchetard).
I'm just worried that if this is the lead single, the rest of the album may not be all that promising, as I would have ranked this as one of the weakest tracks had it been on the last album...