Scooby Doo has got it right. A lot of times, airplanes break. They usually break in the first flight of the day. This is due to several reasons:
1. New crew to the airplane, just finding something new wrong
2. Airplane sitting there for several days
3. The most thorough prefilght is done on the first flight. If there is something wrong, it will usually be found then.
Many times, we are on "hot-standby", where we just sit at the airport, perhaps with the APU on, waiting for a possible trip. This is most often done to back-up other trips. I was in SBA a few weeks ago with a 6:30 am show for a ferry to JAC and we met another crew that morning that was ASAP'd to the airport just to back up our ferry flight! This often happens when an owner has been hit with too many successive "ops reviews" and they are not very happy.
The point: Ops Review sounds a lot better than: Your airplane broke.
One more point. You mentioned MEL's. Airplanes breaking are not always black and white. For example: During the preflight, the pilot finds that one of his AC inverters is not turning on. First, he'll probably shut the airplane down, and restart it to see if it turns on. If not, he'll open the MEL book and consequently contact the PM about the problem. The PM with maintenance may try to troubleshoot the inverter problem on the phone with the pilot. If they can't get it to work, they'll MEL it. However, when an item is MEL'd, there are various limitations placed on the aircraft. The aircraft may not be able to fly at night, maybe it can't fly through icing, maybe it needs longer runways etc. So now the pilot and the PM must review the flight and see if the new limitations affect the flight. During this time, owner services may contact you and tell you an 'ops review' is happenning. Then delays, different aircraft take the trip, you get the picture...
Hope that helps,
beytzim