At first, it seemed like due to the differences in the rating systems in the US and Europe, some titles, which have been given the green light in the US, have been denied in the EU. BUT, with this new change in Microsoft's Windows App guidelines, programs with ratings over PEGI16 and ESRB MATURE will, in fact, be allowed to corrupt the otherwise happy and cheerful atmosphere of the marketplace. This won't happen until December, though. Until then, those titles will still be nonexistent in the store.
Some of the games that fall into this category that Windows 8 tablet users will be able to play include Call of Duty, Assassin's Creed and Skyrim - titles which every normal game store wants to have in its catalog.