I believe that in the GMing book for 3rd edition it was stated that a CR=APL encounter should expend 20% of a party's resources. Therefore the party shouldn't normally face more than 4 encounters per day, because the 5th will exhaust all their resources and a TPK is on the cards(at least, that's the theory). Pathfinder continues the same setup as 3rd edition, so I think that it's fair to say that the game is designed with daily resource expenditure in mind. It might not do this well, but it's there.
This might be true if a day never had more than 4 encounters. We all know they usually either have significantly more than 4 at a "dungeon" location or 1 or 2 for overland travel.
If they were actually building for attrition they would use some sort of per day aggregate CR not per encounter CR and they would limit dungeons and other chained encounters to that challenge level.