I agree that it is dangerous to overestimate the general user's ability to adapt to changes. Microsoft does a lot of focus groups for this very reason. I don't think that Microsoft can cripple itself by never changing the interface, though. Maintaining an identical interface might work for a while, but eventually competitors who weren't afraid to innovate on the UI would win.
I agree about the control panel as well. Search fixes a lot of the issues. I'm glad Windows 8 has kept search working (and arguably improved it).