pshuang,

Yes you are technically correct. What you are doing at that point is very risky. You are correct that for all bumping situations, if there are not enough volunteers, the airline will generally continue to raise the offer (up to a point where they will involuntarily deny boarding). But if someone takes the latest offer before you (assuming that person is the last needed volunteer) because you are hoping for something better, then you are bummed. For me, if the original offer is to my liking, then everything else is gravy.

I don't know about any other airline, but I am glad that AA gives everyone the last, best offer.