How about 100% everything instead of "basically anything", without serious "if's" like "as long as drivers are compatible" ?

If a machine is running, say, windows xp, and it does in a manner that satisfies the owner's need, then it should be able to keep running forever in the same manner, provided that hardware lasts and/or is replaced with adequate spares, not necessarily anything newer.

It's ok if that computer becomes incompatible with newer software because of that.

It's ok if that computer becomes incompatible with newer outside/network services because of that.

It's not ok if that computer stops being able to execute exactly the same process that it could do 10 years ago.

That's exactly how it exists. What you're describing here is reality. If you have a machine running Windows XP and you never change anything, then nothing will change. Software doesn't magically bloat over time, those changes happen with updates that add new features. If you never update things, you'll stay on the same software revision and it will run the same as the day you bought it.

A company I used to work for in 2012 had a Windows 3.11 workstation running some ancient software to support an auxiliary system. Many banks run COBOL on mainframes and haven't changed anything since the 70s.

I'm really confused as to the argument here. If you never update your software and don't expect to browse the Internet, old software works exactly like it did in the past. How do you expect it would change?

The whole issue is that some machines been force-upgraded to windows 10 despite users explicitly (or so they thought) responding multiple times that no, they do not wish to upgrade; and then failing to work correctly because of e.g. driver issues.

This is not acceptable behavior - I can understand automatic upgrades that are fully backwards compatible, e.g. a security patch; but upgrade to windows 10 isn't like that.

Because Microsoft didn't write the drivers for 100% of hardware... and tbh, if a company wants they can pay Microsoft to write those initial drivers, and provided the hardware for testing, iirc, they tend to maintain those drivers between versions. There are plenty of drivers that are written by MS, it's pretty common with Printers iirc, and works pretty damned well.

Because foo pro-audio, or bar cnc-board didn't want to update their drivers, or for that matter, more often than not, had a weird installer that simply didn't follow proper practices, doesn't work in the new version of Windows isn't MS' fault.

Nevertheless, because the chance of something like that happening is clearly higher than 0.0000000001%, Microsoft should simply never do such a drastic upgrade automatically. (So, even within Windows 10, they should not automate all upgrades, because occasionally they will have to include bigger changes.)

Also, users will not understand this, and will, rightly, blame Microsoft.

Any trivial update has a higher than 0.0000000001% chance of failure... if you need that level of specificity, you should disable updates, and network connectivity altogether.

Upgrades aren't always entirely painless and without cost.

If the UI significantly changes, for instance, there will be a time investment needed to re-learn what you need to get work done. (This was a particularly nasty issue for Windows 8, not quite as bad for 10 but there are a few changes for sure.)

If the upgrade fails in any way, there may be significant time spent getting the computer back on-line. Sometimes this takes a very long time.

Software upgrades may actually introduce bugs. In the worst case scenario, some OS software upgrades have actually "bricked" devices (see: Apple iOS 9.3.2). These further impact productivity / take time to work around.

Some very old legacy programs may not work at all. It takes time to implement a new solution for the problem in a new tool. (This isn't a big issue for 7 to 10 from what I've heard, but you do hear this about other upgrades in the past.)

This cost in time is not nothing. If there is no real net benefit, it could end up being a big waste.

Even if people want to upgrade, IMHO the way Microsoft is pushing out the upgrade is quite bad. Usually in the enterprise world, IT departments tend to test new OS releases (and even patch updates) to make sure everything works, before rolling out the updates in the wild. They don't want a patch to break some mission critical software. The cost of that could be huge in some cases.

Even for Windows 7 retail to Windows 10 retail, I could see many people preferring to be cautious. Perhaps they are wanting to wait for a slightly more stable OS (usually the first release of a Windows version is a bit buggy). Some people also might want to test things out first, to make sure there are no problems. Of course there's those that don't want to update because change bad, but I don't think that's all cases.

Furthermore, a fair bit of Windows retail I'm sure is businesses - these tend to be even more cautious than overall consumers. A software update going wrong could cost them money, after all, and "if it ain't broke, don't fix it". I honestly don't think the "rolling updates" model being pushed works for enterprise... even small ones.