@brian.shapiro: Even better than desktop applications being sold through the store, is the idea of desktop applications being updated through system API's. (insert angelic choir/happy dance)
We could see the end of little services that do nothing but ping for updates and nag. Get back in your hole Acrobat! I'll update when I'm good and ready!
And my hope is if that happens eventually we might get rid of the distinction between Desktop apps and Metro apps, and just have both full screen versions and windowed versions of some apps.