TimCLE,

While your logic makes perfect sense it could be very easily exploited. For example, I would book a speculative trip with a return on Thanksgiving Sunday and then try to get out of a change fee to reschedule the trip because the flight is oversold.. And then next trip I would ask for the same favor even though the flight isn't oversold, but just looks like it will be oversold...

It opens up a whole can of worms to allow exceptions, even if that particular exception benefits the airline.