From the article it looks like Rummy was the one overriding the advice from the military.
(snip)
"Military aides on the National Security Council prepared a confidential briefing for Ms. Rice and her deputy, Stephen J. Hadley, that examined what previous nation-building efforts had required.
The review, called “Force Security in Seven Recent Stability Operations,” noted that no single rule of thumb applied in every case. But it underscored a basic principle well known to military planners: However many forces might be required to defeat the foe, maintaining security afterward was determined by an entirely different set of calculations, including the population, the scope of the terrain and the necessary tasks.
If the United States and its allies wanted to maintain the same ratio of peacekeepers to population as it had in Kosovo, the briefing said, they would have to station 480,000 troops in Iraq. If Bosnia was used as benchmark, 364,000 troops would be needed. If Afghanistan served as the model, only 13,900 would be needed in Iraq. The higher numbers were consistent with projections later provided to Congress by Gen. Eric K. Shinseki, then the Army chief of staff, that several hundred thousand troops would be needed in Iraq. But Mr. Rumsfeld dismissed that estimate as off the mark."
If there were 10 options for a field commander, the geniuses in the 5 sided puzzle palace would find 10 more after the war, especially if they were out of service.