Have you read Curtis Saxton's essay on droids, the prequels, and continuity? He pretty much agrees that Threepio is very old, knows a lot more than he lets on, but is incapable of relating what he knows due to his protocol programming. Unlike a biological organism with a "real" mind, Threepio's decision-making ability is strictly limited by the constraints of his programming ... and that makes the whole thing kind of a bittersweet sci-fi tragedy. From a certain point of view.