I think that this touches on what Merry mentioned recently..you have to ask for a 'space available' change, as apposed to a 'standby change'. I forget the exact words, but it was something like that. If it were my airline, then I suppose I would be happy to ship all bums away as quickly as possible, but then, I presume that there are good commercial reasons to let a flight go with empty seats...beats me though.