Originally Posted by
flyerCO
It still has value. You're confusing the fact that no one not on the plane can't buy the seat, with the seat not being sellable. Just because they can't sell it to anyone other then someone on the plane, doesn't mean the value is gone. If there's no value, then how do some airlines offer upgrades in flight? As noted earlier, DL CoC even details a pricing scheme for such upgrade.
They aren't even trying to sell it to someone on the flight (at least not on any flight I've ever been on). So, no value.