1. Japan was allowed to keep it's emperor, that in itself gave "face" to much of the Japanese population and helped legitimize US rule.
2. Japan's ability to resist was crushed. Iraqi's and other Muslim fruitcakes have plenty of resistance left in them.
3. Japan had, and still has, a disciplined population that has a culture with a belief in the rule of the emperor and his law. Retaining the emperor was the crucial move in stabilizing Japan post war. No such parallel exists in Iraq.
4. Both Japan and Germany are not peopled with uneducated barbarians-(even though many Jews and Chinese may disagree). Force of law is usually enough to keep these populations in line. Force of arms is the ONLY thing that keeps most Muslim nations in line.
5. I agree that it will take time to establish order in Iraq, but the rule of law has never really existed in the Middle East. Our work is cut out for us.