For 4Q16:
- iPhone 7 - $650-850
- iPhone 7 Plus - $769-969
Yielded an ASP of $695
4Q2017:
- iPhone X - $1000-1150
- iPhone 8 - $650-850
- iPhone 8 Plus -$800 -950
Yielded an ASP of $796
That is a year-over-year increase of 14.5%, with the only real change being the iPhone X. I agree that some movement of the ASP could be attributed to Apple only offering 2 storage sizes for the iPhone 8s, but really, the price ranges are very similar if the iPhone X is excluded. It could easily be argued that, because Apple also offered their cheapest iPhone ever in 2018, there would be more pressure for ASP to be decreasing [0].
[0] - http://www.asymco.com/2017/09/20/good-better-best/