I hadn't yet thought about all this yet, what, with the massive shift from the desktop to Metro in Windows 8. However, as MSDN explains, Metro applications in Windows 8 can only be installed through the Windows Store. Sideloading will only be enabled for enterprises and developers. I'm also fairly sure the relevant registry key will be easily toggled for us geeks.
"All roads, as the saying goes, lead to the Windows Store," Microsoft writes, "For Metro style apps, that is, the Windows Store is the only means of general distribution (enterprise customers and developers can bypass the store to side-load apps)."
Microsoft mentions the usual benefits, and I'm sure those are all pretty valid. The company does take a 30% cut here, similar to what Apple takes for iOS and Mac OS X. Still, the idea that a vanilla installation of a desktop operating system - without any, probably warranty-voiding registry editing - will be restricted to Microsoft-approved applications doesn't sit well with me.
This doesn't apply to desktop-style applications, but in all honesty, I want to move forward to Metro as soon as possible, since the frantic switching between two paradigms makes me crazy - Metro in and of itself is enough of a shift in user interface that I I'm not too fond of the legacy/Metro dichotomy on top of it.
As Daniel Eran Dilger (sorry for the link to that guy, guys, but credit where it's due) notes, this could possibly affect iTunes as well - in a sort of application store Inception-style craziness. At this point, nothing is known about in-application purchases, but if Microsoft applies the same rules to the Windows Store as Apple enforces in its own application store, then a possible Metro version of iTunes would be in trouble. Purchases through iTunes would require a 30% cut to Microsoft. Basically, Apple would face the same problem Barnes & Noble and Amazon faced in the iOS App Store.
That's some very, very delightful irony right there.