The inflation argument makes no sense with regards to earned miles unless the distance flown also increases with the CPI as well.

Of course the elephant in the room is that a lot of AP points don't come from miles flown but from CC spend, where inflation means that you do earn more points relative to the actual items purchased for the most part, so those points do have a lowering value overtime. It is hard to justify the magnitude of those increases in recent years, at least relative to real inflation. We are talking about AC though so shouldn't be surprised at all.