I don't recall the Windows.old folder ever being mentioned while an Upgrade is occurring, let alone making any guarantee's of it's longevity. You may as well be complaining about the transience of the temp folder- Or it's like the old classic where a businessman was storing all their important documents in their Mac's "Trash".
Well let me educate you. The Windows.old folder is generated after you do a custom install onto a partition with an existing Windows installation. It moves user files into this folder. The dialog literally says "The partition you selected might contain files from a previous Windows installation. If it does, the files and folders will be moved to a folder named Windows.old. You will be able to access the information in Windows.old, but you will not be able to use your previous version of Windows."
So it is a convenience when reinstalling Windows. Not to be relied on, as you should back up your data doing something like this anyway. Windows.old remains permanently in all versions of Windows before Windows 8, although relying on it is foolhardy. It's certainly nothing like the nature of relying on the Trash folder, or the Temp folder, which both are very explicit about being for trash or temporary files....... obviously.
Windows.old contains copies of the windows system data and user profile information. These are migrated to Windows 10 as well but the old versions are kept so the upgrade can be undone. They are not kept so the user can pick through them.
It sounds like we're talking about two different things at this point.
As mentioned I don't recall any dialog being shown referring to the folder being created. It is not intended for users to use and is only there to facilitate downgrades.
We now know this isn't true from what I said at the top of this particular post.
You did not backup or have other copies of the files that were in the Windows.old folder. You were presumably either using files there, keeping files there, or otherwise wanted the files in that folder. The Windows.old folder was deleted because it was a system folder. The fact that you relied on the contents of a system folder doesn't change that it is a system folder for which immutability cannot be assumed- in the same sense as the ability to store and retrieve data on a Hard Disk cannot be assumed to always be possible.
So the first part of that statement is leading onto the absolute truth which is that Windows.old shouldn't be relied on for important information. And then we start getting almost theoretical talking about how you can't trust the HDD at all for even first use. I'm sorry but firstly I agree with your sentiment, and secondly you are making a really weak argument here: yes, technically nothing can be relied upon, but it is crappy behaviour when the system deletes things that probably contain user data without any warning: especially if a programmer
decided it was worth doing this. The worst part for me is that there was a programmer in MS who thought this was a good idea, and clearly didn't consider running it by that many people, or talking to their QA people about this, or whatever would usually be done to assure quality of the product Windows. It just seems like really poor form to me.
If you say something or refer to something as being stupid or bad, putting a disclaimer that you aren't concerned about that stupid or bad feature affecting you in the future doesn't somehow absolve you from defending the original statement.
Well you seem to think I'm defending something which I'm not. Maybe I wasn't as explicit about disclaiming my defence as I could have been... but nevertheless you extrapolated that I was defending this. You guessed what I was thinking and you were wrong.