[Zappin!]

Now now, remember everyone: (and this applies to all airlines): If you look in the contract of carriage that you agree to by act of purchasing your ticket, you will note a clause in that states that seats selected online or when booking your ticket are "requests". You are in no way guaranteed that seat, you only preference it.

If the airline needs to use that seat for a passenger with a disability, by law, they are required to move you. As previously stated, it is true that the only reason why peoples' seats are moved around is in the event of an aircraft swap. This happens all the time; flight loads are analyzed several days in advance and aircraft are swapped to perform flights where they are most efficient.

Let's use this example:

Flight 222 from Chicago to Baltimore is scheduled to be flown by an Airbus 320. This airplane holds about 150 people. Let's say flight 222 is only booked to 100. There are now 50 seats that will be spoiled. Flight 458 from Chicago to Austin is operated on an MD-88 which will hold about 130 passengers. However, this flight is oversold by 15, making a count of 145. Operationally, it makes more sense to now use the A320 for flight 458 and the MD-88 for flight 222. Now no flights are oversold, and no one is denied boarding.

An A320 has 3 by 3 seating while the MD-88 has 2 by 3. Can you see how the A320 will have more middle seats than the MD-88? Also the rows are configured differently so not everyone is going to get the same seat that they requested. The computer system tries to keep people in the same type of seat that they requested, but not everyone will be able to get it because it's a different aircraft and there isn't the same number of window and aisle seats.