The desktop has Aero interface, with some Metro elements here and there. But the tablet interface has a completely Metro interface.
Windows 8 seems like a mixture of two different operating system, rather than a single operating system. If both were Metro, the transition between them wouldn't be so incoherent.
Going from Tile to desktop interface almost seems like going back a few years to Windows 7. Not that there is anything wrong with it. I use it as my primary operating system. But the shift doesn't feel smooth.
If the similarities in the interfaces were increased, the criticism about having two interfaces would be decreased. We have this Aero interface from Vista. That's almost 7 years ago! And it's starting to feel a bit old.
Some people also believe that Microsoft should remove the Desktop version from the ARM version. Microsoft strongly disagrees. And I believe that this disapproval only exists because of UI inconsistencies. They don't match... at all.
But not only will Metro Desktop look great, it would solve these design problems, and also "it just works!".
Metro on desktop and Ribbon is not only possible, but several design concepts have been made by many people. I have looked over them for months, and really liked them. And was sure, that they will make it to the original thing. But that doesn't appears to be the case.
People have been making these concepts since the inception of Zune HD, and were sure that W8 would look something like this. I was looking forward to it too. To an OS which will have a Zune software like feel. Here is the image of header.

May be they will have a fully Metrofied version, by Windows 9. They just wanted the Metro haters, to get a taste for it in 8. And to keep some of that "Windows familiarity".
This is Windows re-imagined, but not fully.











