afe66: If they have sold the seat they have the cash.
If I buy a movie theatre ticket and don't turn up, I expect I have to pay for another full price ticket, so I can't see how they have _lost_ money...
Cynic in me says they will overbook and then make the person who missed pay for another ticket so they have paid twice for the same journey.
Many tickets allow last minute changes in booking, and the expected number of these changes are the number of overbookings. If they didn't do this then they are not flying at capacity.
Hotels also overbook to deal with expected cancellations.

