I recently folded Aces in a tournament. The only reason, was because 3 other people were all in, and aces, despite being a "made" hand, have terrible odds against that many all ins. Pocket pairs in general have less outs, and sometimes, you might find yourself in the position where folding is the correct move, based on odds.
Heads up is an entirely different story. I would never, EVER fold aces or kings, preflop all in heads up. I can't find any logic to do so. You are always the favorite in the scenario.
Oh yeah, Doyle is the man!!!