The problem with all this is that if you actually wait until you get to CLT and then cancel the last leg, whether online or by calling they just do it. There is no repricing at that point and never has been in the 20 years I've been flying AA.

If AA wanted to, they could easily implement a system where "canceling" prompts an add/collect to reprice the ticket. They don't.

So it is easy to understand why someone would think it's illogical to charge to drop the last segment if you call to do so prior to travel but not if you do it after flying the first leg.