Ballpark, that probably still is true. If people buy a replacement every four years, they’ll sell about 240 million a year. That doesn’t require them to attract millions of new users each year.
Now, why do users buy replacements? They may lose them, the devices may break down, Apple and/or app makers may stop supporting them, and new ones are significantly better (even if all updates are, as you claim, small, they still accumulate into big ones over the years)
Thankfully my kids are just aging out of the "we must have the newest iPhone immediately" phase.
https://www.pokernews.com/news/2016/08/poker-pop-culture-015...