An analysis of the Windows 8 app certification requirements by programmer and tech blogger Casey Muratori suggests that games with a rating over PEGI 16 or ESRB Mature will not be allowed on the Windows 8 storefront.
This means we won't be seeing many of the current crop of games on the store, or, given the proliferation of rating-baiting neck-stabbing seen at E3, many of next year's either - not unless publisher's are willing to heavily sanitise their content.
The guidelines are pretty explicit about creating a walled-garden within Microsoft's hitherto anything-goes OS. As section 6.2 of the certificaiton requirements state: "Your app must not contain adult content, and metadata must be appropriate for everyone. Apps with a rating over PEGI 16, ESRB MATURE, or that contain content that would warrant such a rating, are not allowed."
As Kotaku pointed out , this might not be such a problem in the US, where relatively few games receive a mature rating, but it will be very significant in Europe, where games such as Dishonored, Skyrim, Sleeping Dogs, Assassin's Creed, Call of Duty all fall foul of the restriction.
Of course, you'll still be able to buy and install these games on the OS - you just won't be able to get them from the official Windows storefront. So is this a problem? Perhaps - games that don't make the cut won't be able to make use of Windows 8's bespoke features, and by bifurcating the platform Microsoft risks fragmenting the PC gaming marketplace. If games are rated as mature in one location and not in another, will that create stark regional differences? And what's more, from a creative perspective, it may force developers to censor themselves in an attempt to reach that wider audience.
It's a curious direction to take for a platform which prides itself on being open, and the reaction among devs is sure to echo the fears already annunciated by the likes of Gabe Newell , Blizzard's Rob Pardo , Notch and others.