Well, it does obviously have to do with generating sales. But to play devil's advocate, I never have enough battery life, even with a fresh battery. There are incremental improvements, year-over-year, in terms of processor efficiency. I take a lot of photos, and I definitely notice having a 5x optical zoom now. There are details that some people would say are worth upgrading. But it is not the case that all people fit this template.
> Well, it does obviously have to do with generating sales.
I don't think it's that obvious, and I don't think manufacturers count on it ("it" being short length updates)
Instead I think it's about handling competition: say a manufacturer updates their product line every 3 years, should a user that kept their phone for a while need to buy in the middle to last bout, they'll look at the market and see "oh that other manufacturer has released an update to their product line a month ago, so I'm going to buy that instead of a 2yo product from my current manufacturer". The comparison may be done on any kind of metric but it ultimately comes down to what's state of the art at a given point in time.
It doesn't mean the user hasn't kept their previous phone a long time. But to be competitive across the time continuum the product line needs to be fresh enough.
In that sense it generates sale, or rather, helps with retention, not by having one update every year or other year, but by creating the opportunity to stay within one's current brand.
I think leading manufacturers have realised a long time ago that satisfied customers are what generates reliable sales and growth long term. Even Samsung, king of the shiny "innovative"-but-useless bullet-point feature list have somewhat gotten their act together.
