By selecting the F-102 pilot position, Bush would not have been assigned to Vietnam. The F102 was an interceptor that did not see much service there at all. It was nearly obsolete by the time he was proficient to fly it.
If he had been selected for Vietnam, he would have been trained on a more modern aircraft.
bingo.
Not only does Blood have as good point in post 16, you guys are wrong about the F-102 in Vietnam. The Dagger served in Vietnam, and it was dangerous duty:
http://en.wikipedia.org/wiki/F-102_Delta_Dagger#Operational_history