There's a Status of Forces Agreement, you know
However, what Petraeus, Odierno, Ricks and (to a lesser degree) Sullivan seem to be ignoring is that certain Status of Forces Agreement (SOFA) entered into by the US and Iraqi governments this past summer, which committed the US to remove all troops from Iraq by the end of 2011 (with an earlier timeline for removing troops from Iraq's cities). Further, their discussion of alternative timelines completely ignores the national referendum to be held on the SOFA in Iraq in July of this year (the referendum is thought to have been required by Grand Ayatollah Sistani, who insisted that the SOFA must have broad support to receive his ultimate blessing). If Iraqi voters reject the SOFA in the referendum, US forces would have a twelve month timeline for withdrawal starting from that date.
In general, Iraqi opinion at all levels seems to count for surprisingly little in our policy debates about Iraq. This should change. The whole point was to enable the Iraqis to control their country. Other posts on this here and here.
And what's with all the crap coming out of the Pentagon about how we might be there for years and years? Is Obama going to need to fire some people for insubordination? Obama said we're going to leave. The SOFA says we have to leave (and if it's not ratified by the Iraqis, we have to leave sooner). Obviously, the military should give their opinion on what the consequences of leaving would be, and give their opinion about whether they think we should leave or not. And if they disagree strongly enough, they could resign in protest (I wish more had done so under Bush.) But they don't get to decide whether we occupy a foreign country for years and years or not. That decision should be made by the president and congress (which should re-assert its constitutional authority to declare war).