Just yo be clear, Microsoft's guidelines prohibit what would Bebe "Adult only" games by ESRB standards. The problem is when this policy gets translated to other countries, their game policy review boards treat games we would rate as "Mature" like Assassins Creed III or Gears of War as their highest level in their rating system, and in some cases such ad Germany, outright banning them. Its not Microsoft that is causing this, but local standard for rating games. There is nothing inciduous going on.
Actually for the Metro app store it is far more restrictive than that.
http://msdn.microsoft.com/en-us/library/windows/apps/hh694083.aspxsi
That should be the latest guidelines. And apparently it now restricts based on standard ratings boards.
PEGI 16 and up are not allowed.
ESRB Mature and above are not allowed.
Not being rated doesn't excuse an app. either. MS will look at the level of violence, nudity, language, etc. to determine if an unrated title meets the ratings demands.
So, only PEGI 12, ESRB everyone 10+, or Windows Store 12+ and lower are allowed in the store. That's going to cut out a lot of "core" games on its own. Basically anything sold there must be appropriate to be viewed by a 12 year old.
There used to also be restrictions on the size of your app package, but I didn't see it when I went through that page briefly. Although I think this addresses that.
3.8 Your app must meet the basic performance criteria on a low-power computer
The app must launch in 5 seconds or less
The app must suspend in 2 seconds or less
Low-power computers are described in How to test your app with the Windows App Certification Kit.
Which pretty much means, it must be small and lightweight. That eliminates all AAA titles and many independent titles in Steam.
In other words, Steam really has almost nothing to fear from the Metro, excuse me, Windows Store (as it is now called).
Why not have just Steam OS and let users to buy hardware they want plus offer some standard hw. for average joe. I would like to see some highly optimized (windows) OS for gaming and media with some nice GUI.
SingStar affair on EU PSN accounts made me more open for Sony's competition and this could be interesting.
For the same reason Apple doesn't allow you to install any hardware you want. Hardware drivers can become a significant issue once you start introducing user's being able to install any hardware they choose.
Microsoft has invested significant resources in time and money to ensure it can work with as much hardware as possible. Apple are unwilling or unable to do this. After all, a large part of having wide hardware availability is convincing hardware manufacturer's to make and provide drivers for the hardware you want to use. Just look at the state of Linux with regards to drivers. It's better than it was 10 years ago, but it's still rather than hit or miss, especially when you get to less popular pieces of hardware.
I don't image Valve will be wanting to invest quite that much money and effort into not only developing an OS (expensive and time consuming) but then also the effort to support a multitude of hardware devices (as expensive or more so than developing an OS).
Regards,
SB