I have to agree with crasher as well. I have just finished receiving AP6 for Skulls and Shackles and I'm at a crossroads about Wrath of the righteous.
On the one hand I have thoroughly enjoyed our experiences, Pathfinder ACG is on the short list of funnest memories for our group, right up there with Risk Legacy and Battlestar Galactica.
On the other hand however every new release is a close to $200 Canadian commitment to get the full experience, which is really the only reason to play Pathfinder. Lets face it, theres not much game there if you're only buying the base as you miss out on the one true hook of PACG, the character development and boon acquisition.
Having a solid foundation of a base that has everything you need to get started supplemented by adventure expansion packs for each new path would be much more preferable than starting all over again. Even for a retailer perspective, once Iron Gods or whatever the 4th path is shows up, how much space are they going to devote to all these big game base boxes + adventure packs + class decks + unique character add on decks? Especially if there is a continued commitment to two paths a year?