What a silly definition is "disposable computer" ...
It is designed to be disposable. After all if the SSD fails, then you have to replace the logic board, which is often more expensive or close to the expense of buying a new computer. Like how an iPhone is disposable as when it gets to slow, you have to buy a new one, instead of like a computer where you can upgrade it.
If you configure well your iMac, it will works flawlessly for 4-5 years at least. And it will keep an high resale value even after that period, being a good choice for someone with less needs.
Most people don't have the funds to do so. I'd give a baseline iMac 3/4 years before it became outdated. How do you think 2008 era Macs are still useful today? 2GB of ram and a slow 160GB Hard-drive (what my 2008 Macbook had) would not be at all useful by 2012 had the RAM and storage been soldered.
Do you not understand that most users will not have the funds or the ability to upgrade their Mac at purchase to something that will be still good to use into the future? That means when they have to (prematurely) get a new computer, their old machine will be far less desirable.
This is why iOS devices last for a much shorter time than Macs. If you could upgrade the storage or RAM on an iOS device, the iPad 2 for example would be far more useful today. Of course we know why iOS devices are not upgradable (they are designed to be as portable as can be), but the iMac is a DESKTOP machine. EG one that you will only move occasionally.
Resale value will be less for a machine that has hopelessly outdated and non upgradable specifications. The base iMac in a couple of years will be hopelessly outdated.
If it will break, Apple can service it. Not being user serviceable doesn't mean not being serviceable at all !
I know that on a tech geeks forum most of the people are able to do it by himself, but this doesn't reflect the average customers attitude.
Its far less environmentally friendly having to have Apple replace more than just the individual component. Soldering things means that it is more expensive, less environmentally friendly and more likely to get dumped.
Many average customers get their computer person or an upgrade place to fix/upgrade their Mac. Once my warranty period ends stuff Apple's over priced prices, I go elsewhere to get better service, less expensive service and great customer service.
We are in a world where we live beyond our means and the environmental damage and impact of the throwaway society is massive, so now more than any other time is where we should be ensuring that things are repairable in a modular way, upgradable and will last as long as possible. And of course this isn't what apple wants to do, they're a corporation and anything that could cut into their profit margins doesn't matter to them.