I LOVED DOS. I was great at the command line stuff. I think I started at version 2.1 or something like that. But, DOS sure couldn't do what computers do now.
I also agree that the internal numbers of the versions of Windows might be different than the marketing numbers MS puts on them. First was 3.0 and it ran under DOS. Then came 3.1 and it ran under DOS, too. The first version to be an independent OS was 95. It came out in 1995 and was the first 9X OS.
It makes you wonder where version 1.0 was or 2.0. Win 2000 came out in 2000 and XP came out in 2001. They were more marketing names than anything.
Some of my audio drivers have suffered with the newer OS versions. XP is the last one that works for me, and it really sucks, compared to the driver with 95. But, it's still stable.
Microsoft has never been a reverse compatible company. Even their other software would be totally different, when it came out and you had to almost learn it all over again, because things were in different spots. but, I've noticed the same thing with Adobe. I'm a Photoshop user (well, I haven't gone to the online version and never will) and it would always put things in different spots so you'd have to learn the new versions all over again. I HATED that.
But, with MS Word, for instance, you had to keep upgrading, or your version would no longer work. You could get a patch that would allow you to read the newer versions, but that was it. You couldn't edit them. I got all sorts of people sending me newer files than I could even read and it got to the point I just threw in the towel and went to Open Office.