Art,
I work for Allegheny as a dispatch supervisor, and that was not our flight, but maybe I can shed some light on your general questions.
The decision to swap aircraft can be a complex one. It usually takes a minimum of 20-30 minutes to complete an aircraft change, so for any repair of less than that time it is usually not worth the disruption. In addition, a number of people have to be contacted almost simultaneously: both crews; both gates; operations personnel to change gate info in the terminal; rampers who will have to unload and reload bags on one or both aircraft for a second time, while other departing flights wait for their services; fuelers, who may have to be recalled to add or remove fuel based on the pax loads. Dispatch must reissue flight releases, pax must be moved from one gate to another; I've seen the process take more than an hour, just because people get confused, lack of rampers, or the fuelers are busy elsewhere or refilling the trucks. If another aircraft is sitting for two hours, the crew may have left their bags on board as they were supposed to take the same aircaft outbound; before you can swap, you must try to track them down to get their bags off so they don't get lost, but since they aren't expecting to be found, we may not be successful.
I also must decide if I am creating more problems than I am solving; the flight with the broken aircraft may have a backup flight in 90 minutes with plenty of seats, but swapping may put a questionable aircraft on a full flight an hour from now with no good alternative should the aircraft be down for hours. Certain aircraft are also routed to arrive at overnight maintenance bases for work that cannot be deferred for another day, so I sometimes can't use an aircraft sitting right next to the broken one.
It's all a judgement call on my part, based on information from maintenance that may or may not end up being accurate, and the clock is always ticking.
On the issue of flight times being entered in the computer, since we don't have ACARS, crews must call stations on the radio after departure, the station takes the times and records them on a sheet, then enters them into SABRE. A busy night, a ringing phone (or several), demands and distraction from co-workers, and the times may get skipped. We track our aircraft on an Internet system that uses real-time ATC data, so we know where they are, and often have to call the stations in question and remind them to enter the times. Happens many times a day.
Just my 2 cents from my corner of the world. And, ditto to everything AOG-N-It said above....