[Todd]

No, it's not. One thing MS has always done well is backward compatibility. You can still run DOS programs from the 80s on Windows 8 (x86+64). In order to be competitive on ARM, however, they had to massively strip down Windows. They made a very bold move to remove a huge amount of legacy APIs and components in order to get a small footprint with excellent performance characteristics on ARM.

So Windows 8 is really two things: 1. an update to Windows 7 that works well with touch devices running on Intel and AMD hardware and, 2. a Metro only build for ARM that doesn't have a conventional desktop.

One of the great things about W8 over Windows Phone 7 is that you can build native apps using C++, so you can leverage many of the libraries that you couldn't in a managed only environment.

It does take a bit of a shift, though, since you're programming against a new API, Windows Runtime, which is a small subset of what you may be familiar with. In addition, it requires adopting an asynchronous programming model so the UI thread is not impacted. Any operation that nominally takes more than 50ms to complete is mandated to be async only. This means that the file I/O, network, etc. interfaces don't have a synchronous mode.