iPhone X sales volume 20% less than previous iPhone models with the high price tag attached, we can expect stellar profits, which is what Apple is interested (apparently, people are also obliging).
They probably recognised that the Mobile Phone fame is getting over and it would start playing Niche segments with very high price tags looking for higher and higher profits than sales volumes. They might eventually, make major releases every three years as Tim mentioned and annual minor upgrades. In couple of years, iPhones may hit $1500-1700(in some markets with all taxes inclusive, iPhone X has touched this level already) levels.
Others probably have to sell 2-4 flagship devices to match the profit made in single iPhone.
Looks like US market which is very huge in volume is titling away from Apple in this chart. China and Germany not sure about volume.
This is just the FIRST month sale btw....More questions than answers!