It's not just about it "being smart enough". It's about there being actual user demand when it needs to compete with the shiny new model.
A 10 year old iPhone is probably good enough, but is there demand for it? In a vacuum a 10 year old iPhone is good, but why would you pick it if you can have a current one for a reasonable price?
If you have a 2 years old item working and the new 2 months old item offers little advantage over the old one, and its cost is nonzero, an important part of the aggregate demand will stick with the old one...
So, when the models will be "good enough", you will probably use one as the "daily driver" for a long time for consolidated workflows (some of them enabled by the staggering collateral advantages of specialized hardware and obvious advantages of local hardware), and occasionally use other available models for exceptional tasks, and upgrade only when definitely advantageous - like normal goods.
A 10 year old iPhone is probably good enough, but is there demand for it? In a vacuum a 10 year old iPhone is good, but why would you pick it if you can have a current one for a reasonable price?