onedog: if American has a policy that everybody gets the compensation offered to the last volunteer, that's great. I've often wondered if the particular airline I'm flying on has a policy like that.

It is still possible to have a situation where volunteering later rather than sooner gets you higher compensation, though you're taking a risk. Suppose American needs 3 volunteers, and A volunteers when $200 is announced, B volunteers when $300 is announced, and C volunteers when $400 is announced. Now suppose A had not volunteered, and B and C volunteer at the same price points that they did before. American might announce an offer of $500, which A takes (and which you say B and C would then also get). A is of course then taking a chance then that D volunteers when $500 is announced, and American accepts D over A.