I think that this is a valid assessment, but is based upon old facts. The situation in Iraq has improved considerably in the past six months. When failure seemed apparent the suck cost fallacy could be seen in many arguments for "staying the course", however, the significant drop in violence has allowed for plans to reduce troop levels even beyond pre-surge levels. It would seem that the cost-benefit analysis has shifted. Remaining in Iraq to help them achieve a stable government and economy that will not be immediately subject to larger regional influences like Iran has significant benefits, and given the change we're seeing on the ground, the cost is no longer prohibitively high. Even if you disagree with this assessment, you have to note that there are arguments for remaining in Iraq not based upon a sunk cost fallacy.
