The 10 Greatest Operating System Upgrades Ever
Herewith, my idiosyncratic, extremely subjective list of the top ten, in chronological order. (Note that rating upgrades isn't quite the same exercise as rating operating systems, period--for one thing, it sort of rules out 1.0 versions, although I include one anyhow.) I'm pretty sure this isn't exactly the same as your list...
1. Apple DOS 3.1 (1978): Back in 1978, a floppy drive was a pricey, leading-edge peripheral--think of it as the Blu-Ray burner of its day. A surprisingly high percentage of Apple II owners had them--most of us were still futzing around with storing programs and data on tape cassettes--and it was Apple DOS 3.1 that made it possible. Despite the version number, this was the first commercially-available disk operating system for the greatest PC of all time; the earlier iterations never reached the market. You might argue that it wasn't, then, an OS upgrade--but it was certainly a major upgrade to the capabilities of the Apple II, which had been on the market for less than a year.
2. Apparat NewDOS/80 2.0 (1981):