Three reasons why the 72-hour rule is really not necessary:

1. Now it is $900 to upgrade round trip on most international tickets (which was not the case when the rule went into effect) so that really limits the number of people who would try it.

2. The reservation system is so sophisticated in catching other rule violations, it should be able to spot suspicious booking patterns.

3. The 72-hour rule could be made to apply only if there were no seats available at any time within seven days before the flight. As long as seats are available revenue is not being lost, even if there were a fraudulent booking.