An interesting point, but I'm not sure it applies. Microsoft knew they could never really commoditize computing with a command-line OS, so Windows was an absolute necessity. It was demanded by literally billions of customers, most of whom didn't even know they needed it. Even then, Windows took several years and three major versions before it really caught on.

These days, desktop computers are as ubiquitous as they are ever going to get, and few people are demanding a replacement for the traditional Windows UI on the desktop. Unlike DOS, what Microsoft has is good enough for the mass desktop/laptop market. The fact that it's not good enough for mobile does not in any way justify tinkering with their successful desktop strategy. IMO, what we're seeing is yet another panicked, reactionary twitch from the Ballmer executive suite.

Makes sense. The first 3 versions of Windows ran on top of DOS. This first version of Metro runs "on top" of a classic Windows desktop... And both were responses to products Apple launched (Lisa/Macintosh and the iPad). What Microsoft is doing is using Windows as the platform that introduces Windows+1 much like it did with DOS.