I’ll respond to the last item - Perception.
I do think this latest round of IPhones (and Samsung phones) have reached a level of quality, and more importantly Durability, that I would guess people will start holding onto their phones longer. So I could see a slowdown of sales in the US, just because phones are higher quality.
Interesting that you mentioned this. Did you see the post from swordmaker about the class action lawsuit from frustrated 4s customers? Apple could end support for older phones thereby forcing customers to buy newer phones. They did this with my ipad and apparently the recent iPhone OS update degraded the functionality of the 4s. So the hardware and battery might be just fine but the phone will be unsupported.
Samsung quality? Must be a joke. I have an S5 and after one year the AMOLED display started to show signs of a bad burnout. Now the display looks terrible. This phone is supposed to be waterproof, but the USB connector cap broke off after one month and the case now looks like it has been in a war, although I always took great care of it.
Same story with a Samsung Grand Prime. Never worked well and they refused to do any repair under warranty, claiming that I damaged it.