As they say, it is very easy to criticise someone else for at least trying something and very hard to solve it yourself. I will fully admit that I have no better ideas for how to both keep the classic desktop but also integrate the new touch screen "metro" elements into it.
I really do have to say that I think Apple has the "best" solution right now. iOS for touch devices (iPad, iPhone, iPod) and OS X for desktop. Then they get to sit back and make an absolutely wonderful user experience for both scenarios without worrying about the potential crossover.
If I was in charge of Windows that is likely what I would do. Make Windows for Desktop and Windows for Touch, with starkly different UIs and designs, but with some emulation layer so people can run a touch app on the desktop (in like a sandbox window).
Frankly Windows Desktop has a LOT of crust on it. Go look at Control Panel. They have UIs unchanged since Windows 9x (Mouse, Keyboard, etc), then they have UIs added in XP (Firewall), then different ones added in Vista (Action Centre, etc), and now in 8 we have "Change PC Settings" which is another UI concept again.
If you've ever used OS X for any amount of time, the thing is just polished and consistent from top to bottom. I mean go compare OS X "Preferences" to Control Panel on Windows 8, and Apple manage to get that kind of consistent polish all over the place.
Microsoft cannot kill the Windows Desktop as much as they might wish, so for the love of god go through from top to bottom and modernise it. Control Panel = Gone. Folder Options = Gone. Device Manage = Gone.