Actually I think this was a very smart move by Obama's people. Think about it, now they have a built in excuse for when they lose. I can hear it now "If he had chosen Hillary, then the Dems would have won."
And actually, this puts Hillary in a pretty good spot. If by some miracle Everybody looks past all of BO's faults and the fact that he doesn't stand for anything except "change", and he wins, then Hillary can say that she knew he was going to win, and that is why she "let" him have the nomination. If (and when) he loses, Hillary can step in and say "See, I told you so", and try to run with that for the next election. So even if BO had asked her to be his running mate, I doubt that she would have accepted, when the alternative is just too good for her.