I would not be surprised to see a better hand from the other guy if I called his shove. But, that's not to say that I wouldn't call him either. Depends on my read of his style. As you say, if this is the first time he's done it, and he's been at the table for a while, I'm likely not calling.
But if he's been generally aggressive, or if he's brand new to the table, and if this is the only playable hand I've gotten in an hour (which seems to happen a lot), and if I've got roughly twice his stack, I'm more likely to call. AJs isn't the best hand in the deck, but it's nothing to spit at either. It's actually in the top 5%, only a 2:1 dog to KK, and basically a coin flip w/ TT.
I HATE missed opportunities that lead to blinding out of a tournament. I also play tournaments to win, not just to place. Almost as bad as blinding out before the bubble, is just making my buy-in back after spending hours grinding away in a tournament.
And, I've seen pocket Aces lose a lot! The only thing that's for sure in poker is that you've spent some time playing cards. Everything else is subject to chance.
I just played a hand where I lost (all-in) with AK (to TT), but would have won with AJ.