The advantages of AK are mostly in it's preflop value:
1. Fold equity. This is the biggest advantage of AK. For me it is almost alway a REraising hand preflop. For you to take advantage of this, you MUST play it aggressively (your opponent must fold). Small pairs can't really call you for fear that you have a bigger pair when you play it aggressively. If you do get called, even by something like QQ, you are still only a slight dog.
2. Pre-flop dominating hand. This is mostly applicable against donks who will call you with Ax soooooded. Inversely, you are only really dominated vs AA or KK (and you have about 30% vs KK).
3. Post flop your top pair always has top kicker when you hit.
Obviously when your opponent goes all in he has neutralized AK's biggest advantage as he can no longer fold. Against two random cards that don't include either and ace or a king you are not that big of a favorite with five to come, as other posters pointed out. But you don't ever really want to be calling an all in with very many hands (AA and KK excepted)-- YOU want to be the one doing the raising or pushing.
Just to look at it another way, let's compare AK to a small pair, say 55.
AK is a dominating hand. IF your raise is called you are (most likely) either:
1. way ahead (vs. a weaker ace)
OR
2. in a 50/50ish race.
With 55 you are (most likely) either:
1. way behind (vs. a bigger pair)
OR
2. in a 50/50ish race.
See the difference?