@W3bbo: Okay , I get what you are saying. Sorry about my previous reply. However:
The main reason they have the difference in 'native' controls and 'SilverLight' controls on WP7 is because the OS itself and the DEV tools were developed at the same point in time (because if the tight schedule).
There would be no reason for updating the 'native' controls, why not just only update the SilverLight controls? The only thing they then have to do is reduce the usage of native controls in WP7 and start using the SilverLight ones by default when adding new features to the OS. And I'm thinking they are already doing that.
Running WP7 applications on Windows 8 would only be a matter of running SilverLight on Windows 8 and interpreting the XAML in a different way if the screen resolution is different (large windows screen). [It might need to be duplicated or recompiled but I'm taking the optimistic side here]
Running WP7 native hubs/applications on Windows 8 would be harder, but also less appealing to the dev audience and less needed as long as they provide a good way to port SilverLight based applications to Windows 8 (and Xbox360)