Why do you need a single OS?
Not that I gave you a -1, but seriously, the two have completely different user markets that want different input devices, different usage styles, different horsepower requirements, etc. It makes little sense to try and address both of these two vastly different markets with the same OS.
The problem is that in order to serve two vastly different markets like that, you end up compromising on the features that have to be different between the two - either you "force" one group of users to do things the same way as the other group, or you screw it up for both. Either way you end up alienating at least one of the markets. That's just bad business.
I understand that Microsoft is trying to get into the tablet game, but they ought to offer Windows 8 as tablet-focused and NOT try to force it to the desktop. All it is going to do is frustrate the power users and developers who are Microsoft's core.
