True, but if there are other issues this will be the first one cancelled. I had a flight on Monday where there were only 7 seats taken when I checked in about 4 hours before the flight. 30 minutes later, it was cancelled because of maintenance. I don't doubt that they had a mechanical issue on a plane, but when it came time to choose which one to cancel, I am sure they looked at the load on my flight (and also considered the load on the plane coming back).