This is a reflection of the fans and not the offered devices.
If the X did not exist, the vain collection would have made the 8 a sell out and in huge demand for months, its about owning the newest apple device, not what the device is. Such is the ownership of the iPhone .
Cook is depending on this, cause even if he raises prices more....it will sell, sad reflection of the consumer base, and the X is not the best iPhone to launch. In my opinion the 4 was so far head of what was offered on at the time , the x is playing catchup to the S8. Problem the S9 will raise the bar, while cook will want to milk the X for the next 3-4 years