The flat theme on the desktop is clearly designed to follow the same flat theme of Metro so obviously it is related design wise. I'm not sure how you can say it is "entirely unrelated".
Obviously we would just have to agree to disagree on this. None of us are going to change anyone else's mind, so this discussion is pointless. My experience with Windows 8 is that I hate it, even after trying for a long time to like it. Your experience might be that you like it. I guess we would have to wait and see how this plays out.
Some idiot at Microsoft thought that this "flat theme" was a good idea. I have no idea why because it does not make usability easier. I talked to the Visual Studio developers at Build and they did not like it either but were mandated to go forward with it. It just takes one idiot (Sinofsky with windows 8) to make a bad idea become the norm. I think they have run out of other ideas so the only answer from the people they hire is to tweak a perfectly good User Interface and make it worse (going backwards). The whole point in making a button appear 3D is to mimic the physical world and allow users to imagine a real button. Why are all the smart people at Microsoft silent when these stupid ideas surface. I hope the new CEO and Gates get things back to normal.