The original MacOS design wasn't 'perfect' but it was very, very good. And Apple messed with it at their peril. They gave themselves a similar bar with iOS 1.0 - they know a lot about interaction design, and how to make a UI feel smooth and intuitive, and they aren't going to scrap all of those good decisions for the sake of looking new.

By contrast Microsoft have some interesting design ideas but they abandon them in the very next major version in favour of trying something else, which is jarring for users and doesn't inspire trust.