One of the changes our forces in Iraq are undergoing is the shift from division size units to battalion size units. These are then subdivided into even smaller units used to embed with Iraqi forces. In the process, we greatly reduce the logistics tail for a given amount of combat force. This improved tooth to tail ratio will lessen the demands on our forces. We will no longer need so many of those convoys bringing materiel to our troops with their vulnerability to roadside bombs.
This is a point that Bing West made in his book, The March Up, Taking Baghdad With the United States Marines. The Marine forces, with a much lighter logistics train, got to Baghdad before the mechanized forces of the Army. It was a Marine force that pulled down Saddam's statue. Basing your forces around an all-purpose division concept means you have forces with limited utility to a specific task. We need more civil affairs troops, not Patriot missile batteries, to fight an insurgency with no aircraft. This is a big part of the transformation Donald Rumsfeld instituted and so many generals have resisted. Battalions are not led by generals, rather they are led by lower ranking officers. Consider this question, is reducing the top-heavy organization of the Army a good thing for the nation and a bad thing for those surplus generals?
Predicting our troop needs on an obsolete model will not yield accurate results. We need to base our predictions on the current model.