So Gabe Newell did not overreact on Windows 8... because of what Microsoft might do in Windows 9.
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.
You can sideload store apps in Windows 8 relatively easy. What you need is the .appx file for the app and powershell. Using the PS prompt you can sign up for a developer license (free, renewed each month) and deploy the .appx file containing the app. No store updates this way, but the app appears on the start menu and works normally.
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.
We had a team prepare for a demo on WinRT tablets in the US. They went overseas to do the demo - license expired in route. No connectivity; couldn't VPN in due to no WinRT VPN client, had to drop that part of the demo. Huge pain, no gain.
Steam is more an open platform than Microsoft App Store? Really? While I like Steam, it seems to me to be the most closed and opaque of all the various app stores around
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.
These restrictions are already in place on Windows RT like the MS Surface, right? You can't install apps that use the desktop, and you can't sideload any Metro apps.
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.