On the Mac side, people haven't really learned the benefits of standard look and feel to the degree they have on Windows. Not to say there's no standardization, but in general, Mac apps are a chance for developers to strut their stuff and display cute widgets. MS has spent many multiples of what Apple has spent on UX design, so you get a slightly less flashy, but overall more usable, set of applications on Windows, because of the way the APIs are structured.
Where this style of UI really shines is for the iPhone. I don't think anybody still seriously thinks that Mac is preeminent on the desktop. That hasn't been true since .NET, let alone WPF. But on the iOS...Apple's dominance is clear.