Part of the reason is that the repair or replacement cost doesn't bother me enough for it to be worth putting it in a case (which is a privilege of being a well-paid software engineer; I understand not everyone can afford to have the same priorities).
But at any rate, if I were more price-conscious, repairability would matter much more than a longer warranty, since with repairability I could fix problems that are my own fault just as well as ones due to normal lifespan issues.
Do other people have different experience?
How long would an iPhone last without abuse?