Bush's decision to analogize the US presence in Iraq to the one in South Korea is truly telling. The two situations could hardly resemble each other less. If we take Nouri al-Maliki's government to be something like Syngman Rhee's dictatorship at the core of the analogy, then who plays the role of the North Koreans? How do the Kurds and the Sunnis fit into the picture? Where's the USSR? Approve of it or not, the decades-long American military presence in South Korea has a very clear-cut rationale -- it was there to defend America's South Korean client regime from the USSR's North Korean client regime and now inertia keeps it there because the DPRK still exists even if the ROK doesn't really need outside protection.
In Iraq, none of this stands up at all. It's just a raw expression of a desire to keep our troops in Iraq more-or-less forever. For no real reason. In a country where they're clearly not wanted by either the Sunni Arabs or the Shiites, and where our "allies" in the government are as much Iran's proxies as ours.