It was not a long speech, but it summed up MacArthur's reasoning on why he had advocated taking the war into China. It ended with a most-quoted line about old soldiers fading away. The entire speech is here.
But his dismissal stuck, and Truman is generally given his due these days. As commander-in-chief, a president can't very well have his top general loudly advocating an alternative military strategy in the middle of a war, however wrong the general considers the president to be.
But there may have been more to it than mere insubordination. If author and Korea specialist Bruce Cumings is right, Truman also wanted a more reliable commander in the field in case he -- Turman -- decided to use atomic bombs.
"The US came closest to using atomic weapons in April 1951, when Truman removed MacArthur," wrote Cumings in Le Monde Diplomatique (December 2004). "Although much related to this episode is still classified, it is now clear that Truman did not remove MacArthur simply because of his repeated insubordination, but because he wanted a reliable commander on the scene should Washington decide to use nuclear weapons; Truman traded MacArthur for his atomic policies."
Fortunately, the United States refrained from those "atomic policies," whatever they might have been. The entire article is here.
Interestingly, MacArthur's father, Gen. Arthur MacArthur, had a run-in with civilian authority as well -- namely future president William Howard Taft, the first US civilian governor of the Philippines -- and was ultimately transfered from his command in that new US territory.