My guess is that Apple can replace them 7 times and still be ahead profit-wise.
I once had an expensive brand of computer mouse. After eight months the mouse failed. Later I bought another mouse from the same brand. The mouse failed after 14 months. I stopped buying from the brand. The same thing can happen to Apple, and they need to be careful about the quality of the products they sale when they charge premium prices.
Pretty sure that's on the low side. Plus, logistics cost of dealing with replacements and such adds far more than just absolute BOM cost.
Take a look at the cost estimates that most folks do on smartphones (Ex. https://www.techinsights.com/blog/samsung-galaxy-s10-teardow...). Apple isn't undercutting other companies by $300+.