Why doesn't MS do this on Windows 8 on Desktops

One of the big things I hate about Windows 8 is the fact that every app is fullscreen. I've written why here (warning: not The Verge, but a shameless plug of my blog). Basically, I hate Windows 8 multitasking and fullscreen-ness.

So how about this:

It's a regular Windows 8 screenshot with a Start Button.

When you start up your computer, it loads the desktop view by default. Instead of a wallpaper and shortcuts, the actual space of the desktop wallpaper is replaced by Metro. So you have a start button (no menu) and no desktop shortcuts or wallpaper: just Metro in that space. You can add folder shortcuts, you have your apps and more. No more messy, unorganised desktop.

When you open a Metro app, the Metro background goes a bit translucent and the app opens in a Window. So for example, below the Mail app is in a window and so is Google Chrome. An old app and a new app, side by side, and it uses the best (current) way to use a mouse and keyboard, which imo is in a window, not fullscreen.

This would only happen on the desktop version, not the ARM version because it would be harder to use touch, but it would mean that you get cross-platform benefits of Windows 8 on tablet and also a seamless access to old apps. I hate the current flipping between old and new apps and I also hate things like fullscreen Weather apps. So if they had Windows, it would work with tablets and also desktops and laptops.

These mockups are obviously quick MS Paint jobs (ironically from the Windows 8 Preview), so excuse me for their terribleness, but I hope it gives you an idea of what I'm saying.

I know I'm not the first to think of this, but it would be the only solution to the mess that is Windows 8 on desktops with no touchscreen, in my opinion.

Feel free to tell me why this is dumb in the comments, but please give me reasons. Also, does anyone like Metro on Desktops?