Re: so difficult in fact that Debian have been doing it
"I think the MS install base is a little larger than the Debian one, and also has less consumer users."
The scale effect might come into play with download speeds and to some extent the speed of checking for updates. But as Stuart said, the installed base is very diverse: from the Raspberry Pi upwards to larger server installations. I think we can reasonably conclude that scale wouldn't shake out many if any hidden quality problems. And having installed updates on both Windows and Linux I know from experience that the latter are still faster even if you disregard the download speeds.