You really don't understand Vietnam do you?
They won for a multitude of reason:
1. The US population had little or no knowledge of what was really going on over there. This led many people to either want to end the war, or believe that we were losing. This made the politicians want to end the war, and the war ended.
2. Over in Vietnam, the Vietcong were not using traditional war tactics. They used the infamous tunnel system, which allowed them to bring troops behind our lines as we advanced, making these advances dangerous. This demoralized our troops, and you can figure out where that led to.
3. They had more than a tank and some crop dusters. They had more than a dozen of the best fighter in the world at the time (opinion, not fact), and were fighting for their land and families. Our troops, while better equipped, where in a demoralizing land of constant transisions from hot to wet and back, and were only fighting because a man a hundred miles from the front said they had to.
And on the matters at hand:
Did TOm ever actually make that trip to Europe? Ten bucks he did, and found the Earth to be Round.