[mikeash]

If you had bought the trip you actually wanted to take, you would have paid more. Further, it would have left a seat open on the second flight which they might have sold to somebody else, making even more money still.

Of course, the second flight probably isn't 100% sold out, and you might have gone with a competitor or not taken the trip at a higher price. But they don't necessarily see that, much like music labels don't necessarily understand that every instance of piracy is not a lost sale.