That's fair. I'm assuming the majority case is simply: device breaks, can't be fixed easily, gets thrown away. I think we'd need some actual data to have a meaningful discussion about it.
That's a reasonable assumption. Anecdotally, on my local high street, there are at least 5 places--one official Apple service centre (not an Apple Store)--that offer battery and screen replacement for all mobile devices and tablets. At least 3 have been there for more than 5 years, including the official Apple one. There must be some demand for them all to survive.
- Users generally replace a device less often than replace a part.
- Users usually throw away a part, but not a device. As a matter of fact resales value of Apple devices are higher than for other makers.
- Apple have the mean to recycle trade-in devices and not landfill them. Users may not.
- Devices with replaceable parts may have shorter lifecycle than the ones without, since they are more brittle and complex.
About the only argument for replaceable part is user freedom to fix their devices.