Exactly. Two things. If I can't resell my one or two year old iPhone for a decent price, I'm going to worry a bit more about buying a new one. Also the secondary market allowed Apple and the carriers to offer significant trade in value. These trade ins probably outnumber those of us who personally find a buyer of our used phones. But it is crucial part of the whole process of getting consumers to buy new phones. And second the SE price was a clear indication to me that in 2016 Apple realized it needed to put some cheaper phones out there. The SE has the same CPU as the 6S and yet costs $250 less! That says to me that Apple is setting up some room for the 7 to be a bit cheaper than the 6S.
Prices this fall can be:
SE: $399 (as it is priced now)
6S: $499 (+$100 for plus maybe something where the plus starts at 64gb)
7: $599 (+$100 for plus which comes with dual camera) (+100 gets you 128gb storage)
The 6 gets discontinued. There is no point to having three models (each with a plus version) with nearly exactly the same form factor, plus if you keep the 6 around you have to explain how its CPU is worse than the SE and Apple sets itself up for problems down the road having to support the A8 processor for another year (like into 2020 if it plans on selling new 6 phones in 2017).
