Srbmod raises an interesting point, even with an all volunteer service, the US still seems to balk at the thought of casualties, arguably that may have allowed OBL
and his top cronies to bribe their way out of Afghanistan, past those proxy troops of the Northern Alliance, (any quick look at the history of the place would have warned against using the local forces, still the US preferred them to their own and the 1000's of offered NATO troops, say what you like about France and Germany, but their troops would not be firing on US troops, like some of the 'allied' forces from 2001 are now).
So if they were not willing to risk major casualties in direct response to Sept 11th, what does that say?
To a certain Mr Hussein of Baghdad, it says don't let your forces get zapped by airpower in the desert, but make 'The Sons Of Dogs' (to use the Iraqi slang), fight for every street of every Iraqi city, like Somalia but much worse.
Like his tactics of 1991, it might not work, but somewhere, sometime, it will.
It is not only the structure of the military today that mitigates against bringing back the draft.
It looks to be politically unacceptable too.
But if North Korea kicks off, heavy casualties are unavoidable, none of this is a dig at the US forces, rather the body politic, easy to be gung-ho when every action has been a high tech turkey shoot, so far anyhow.