That said, Steam right now is more of an open platform that the Microsoft App Store. Even if Microsoft put up big, scary warnings, they really should allow the side-loading of Metro apps or have a Control Panel option to allow for their installation.
Microsoft even provides a PowerShell script that automates this installation each time you build a Windows Store app in Visual Studio along with the .appx file.
OK.
>What you need is the .appx file for the app and powershell
what
Great, my OS is now timebombed to permit me to only install what I want on it at Microsoft's pleasure.
How on earth is this "easy" compared to "compile it and you can run it forever" like Windows has been since Windows existed?
(Also: what happens when Windows 8 support is "sunset"? You just can't use that computer anymore? Jeez.)
Look at Steam Greenlight, which provides a very slim chance an indie game might get onto steam: http://steamcommunity.com/greenlight
Basically the rules seem to be lots of people apply, everyone pays, and you might get on if we like you, we will set your price and tell you the revenue split. In particular, a very small number of submitted apps get onto the store.
On the other hand, getting into the windows app store seems to have much more clearly defined rules, and Microsoft is trying everything they can to get more games on.
The Windows App Store is more inclusive, but there is no distribution outside of their ecosystem unless you have an enterprise license.