If the FF program is little more than a way to sell distant future seats at a big discount, then devaluing continually makes perfect sense. I believe that Southwest's program fits this description more closely than any traditional FF program.
I'm not sure the airlines would like that description. It is a little too intriguing to the attorney who would file a class action lawsuit that the devaluation was so extreme that it violated a promise to provide that future travel at a rate reasonably consistent with the award travel rate existing at the time the customer obtained the miles/points
