Most of the troops you identify are supporting deployments worldwide or are surrvcing in under-strength combat units. There is a useful presentation of the U.S. order of battle at:
http://www.geocities.com/Pentagon/9059/usaob.html
Also, James F. Dunnigan reports on the hollowing out of U.S. ground forces regularly on his Strategy Page site.
According to the 2004 Quadrennial Review, the U.S. is supposed to be able to fight two theater wars simultaneously, one on the offensive, one on the defensive. With moree than half of U.S. ground forces tied down in Iraq indefinitely, the ability to do so is questionable.
Conservatives have paid a high price for Iraq. We've lost Congress. The Bush tax cuts expire in 2010. Social Security reform is dead, at least for the next two years. It's questionable whether any Republican can win the White House in 2008 if saddled with the Iraq albatross.
Lyndon Johnson was faced with a similar dilemma in 1968. As a result of Vietnam, Republicans have controlled the White House for 26 of the last 38 years.
We could withdraw our forces from Iraq if we can solve the strategic dilemma in Iran. Those troops are in Iraq because the persistent interference by Iran/Syria.
Once the Mullahs are destroyed and Syria is out of the picture, Iraq can handle what's left of the Sunni and Shia terrorist.