I can understand what they wanted to do. The idea of a unified experience is, on the surface, a pleasant idea.
Steve Balmer wasn't wrong about that, he just didn't understand that it doesn't work. Tablets, phones, and PCs are all *very* different beasts used for very different purposes.
Honestly, he should have known better. Trying to make things like phones, tablets, and PCs use exactly the same interface is literally like believing that Excel and Word should have the same interface. They might have the same look and feel, but because they are different apps performing completely different things trying to shoehorn both into exactly the same interface (not just common elements, but exactly the same interface in all respects) would be ludicrous. Anyone who knows anything about user interfaces should know better, and I'm pretty sure Balmer knew better but still tried to force it to promote Microsoft's Windows-everywhere strategy.
Fortunately, the new leadership at Microsoft understand the mistake and are working to correct it.
Not sure I agree. On the one hand, Nadella seems to better recognize the priority of cloud computing and Microsoft as a services company that sells software and not a software company that offers services. On the other hand, the "one Windows" strategy continues to smell like "Windows-everywhere" just in a different form. Yes, its not exactly the same and "one Windows" doesn't specifically presume identical interfaces across the platform. But its still this belief that one thing can be the right thing everywhere, and that one thing is Windows.
Personally, I think they learned the wrong lesson from the failure of Windows RT. I think that only reinforced their belief that anything short of full 100% Windows is something consumers will treat as a toy and will not accept. But that had more to do with the limitations of RT, and less with the idea that only full versions of Windows are "good enough" for consumers. It'll be interesting to see how Windows Mobile fares under Nadella and the one-Windows strategy in the long term. Does one-Windows leave enough latitude for Windows Mobile to evolve independently and agilely verses competitors (IOS, Android)? We'll see.