The differences in Iraq are less about the concrete plans for what to do next than about our perception of the quality of the judgment of the candidates.
Unfortunately, Iraq is such a wretched situation that there are no good answers. Pull out prematurely and there's the risk that the country will decend into outright civil war. Don't pull out and we'll keep bleeding billions of dollars and thousands of American lives, while possibly acting as the irritant that prevents a more stable situation to take hold. There's no patently good plan for mitigating the harm we caused with our invasion. Thus, the discussion of Iraq isn't about specific plans for moving forward, which are all going to be unavoidably unappealing, but rather about whether the candidate can be trusted to make sensible decisions, in general, when it comes to foreign policy.
That's why I'll be voting for Obama. I'm not certain he'll handle the Iraq catastrophe any better than McCain. But I am certain that he's less likely to push our country into a similarly frivolous and disastrous war in Iran (or Syria or North Korea). McCain has convinced me, again and again, that he's just not smart enough, honest enough, and open-minded enough to learn any fundamental lessons from the Iraq mistake. He continues to see the errors of the Bush foreign policy as simply quibbling problems of poor military tactics, rather than the core problem of us having started a war when there were still plenty of other viable options.
Because of McCain's weak intellect and lack of moral fiber, I just don't trust him with the military. Obama doesn't have to be far removed from McCain on the "going forward" strategy for Iraq to be far removed from him when it comes to overall foreign policy vision. Obama has shown far more healthy skepticism about the usefulness of war as a tool for foreign policy, and that's almost single-handedly enough reason to vote for him.