Because they demonstrated that the U.S. could stand up to totalitarianism, and that Americans would put their lives on the line to keep more people from becoming subjects of the Great Leader?
Because the military buildup projected in NSC-68--the build-up that Acheson thought was very necessary--had not a snowball's chance in hell of getting through the Congress before Kim Il Sung's tanks rolled south?
Because Harry Truman repeatedly and publicly told Acheson that he did good in the crisis at the start of the Korean War?
My assessment is that these three reasons weighed about equally in Acheson's mind in impelling him toward the judgment that those two weeks were "glorious." But I could be wrong: Acheson's mind is hard to read--I still don't know what he intended in the summer of 1941 in closing off exports of oil to Japan...
Brad DeLong