Just the names imply the difference: Truman made a pronouncement, Marshall suggested a strategy. As far as these two items are concerned, both entail nation-building, but it does not appear that the conditions "free from coercion" lasted long in Greece. Though "free" from communism, A military dictatorship began to rule Greece by 1967, a scant twenty years after Truman's Doctrine was uttered.
As for Turkey, well... was Truman speaking of the Armenians in Turkey being free from a way of life free from coercion? The Greeks in Turkey? The Jews? The Kurds? As sarcastic as I sound on this issue, I am glad that Turkey remains to this day less coercive than most states that were spun from the remains of the Ottoman Empire. But I remain unconvinced. Was it the Truman Doctrine that made this so? What is the legacy of the Truman Doctrine? Is it simply US Air Force Bases in Turkey and a sweet duty station at Souda Bay for the US Navy? Has the Truman Doctrine has stood the test of time? The idealistic side of me likes the rhetoric of it, The Dubya Doctrine echoes Truman's... but what of success? I believe the Marshall Plan can demonstrate its success; Berlin alone became a beacon to East Berliners - something that made people willing to risk it all to get there from the other side of the political-economic-ideological divide... but what about this Truman Doctrine? Did it meet its aim as a "policy of the United States to support free peoples who are resisting attempted subjugation..." or was the ending of that statement a built- in loop hole, "...by armed minorities or by outside pressures."
I suppose that working out their destinies in their own way was successful, if a military junta was the way that the Greeks wanted to work things out on their way to democracy. And since the groups in Turkey I mentioned above were not minorities ruling the Turks, that could be a success - majority did and does rule in Turkey. But was it on the merits or action of the Truman Doctrine?