Matthew Yglesias explains succinctly what is wrong with this comparison:
...the difference between Iraq and South Korea isn't just that post-armistice our troops stopped taking casualties in Korea. The bigger difference is that a US military presence in Korea was part of a larger strategic doctrine -- defending the anti-Communist ROK government from the Communist government in Pyongyang as part of a larger strategy of containment -- that made sense. What we're doing in the Gulf right now is driven by confusion, hubris, and vainglory.The more apt comparison, of course, was and still this one: that Iraq is Vietnam on speed.