The $25 customer service vouchers are really a hit and miss propostion when you volunteer. I get them about 10% of the time and have learned not to expect them.

I've been bumped 5 times so far this year, but I have probably volunteered at least 2-3 times that when I had an indication the flight would be full (I check seats left for sale before I head out).

Could there have been a last minute aircraft change that might have changed the seat availability (i.e. larger plane with empty seat to smaller plane with no empty seats)?