Rummy has resisted increasing the size of the Army because he is enthralled with the arguments of the "transformationists". Part of the way that he is trying to address this problem is in how he has reorganized the Army into brigade combat teams. This is a good reform, but we probably should have added another 100,000 actives to the Army and Marines after 9/11 (and provided whatever incentives needed to get up to that strength). It doesn't help that it often seems like he is playing chess without looking at the pieces.
Rummy can resist all he wants if Congress authorized 1 or 100,000 more troops he would have to eat them. He is not the final word on this issue.
The question is can we add another 100,000 troops in an essentially full employment economy without increasing the pay substantially (50+%) to get the recruits or going to a draft.