A couple of weeks ago analysis from tech blogger Casey Muratori revealed restrictions in the Windows Store's certification requirements that would exclude Mature games from the Windows 8 storefront. The US ESRB Mature rating overlaps with Europe's PEGI 18 rating. As a result, major releases like Dishonored and Skyrim would be excluded from the shop in the EU.
Gizmodo report that Microsoft have decided to change the policy to allow for the inclusion of ESRB "Mature" and PEGI 18 rated games. Hooray! Unfortunately, it'll take time. Windows Corporate VP of Web Services Antoine Leblond estimates that the shift will happen in December, which is still too late to meet the release dates of Far Cry 3, Hitman: Absolution and Assassin's Creed 3.
Steam, Origin and other clients and online stores will still work on the new OS, of course, but it's a bump in the road for the OS that Gabe Newell famously dubbed "a catastrophe for everyone in the PC space." Windows 8 launches today.