All mobile users in the US (some 234 million) would be a part of one ecosystem in about 2 more years. That’s less than the life cycle of the typical mobile contract (and thus the life of one phone). Put another way, by the time a new buyer today is ready to buy the replacement to their phone the market will be saturated.
This implies the mode of competition will be changing to smartphone replacement rather than smartphone adoption.
Call it iOS loyalty or customer retention. This is where Apple is better than other vendors.