That probably isn't any problem for those living in North America as "AO" rated titles are not really sold anywhere by anyone. Europe, however, may have a bit more of an issue with this witht he PEGI 18+ rating.
This rating is applied to many titles that we here in the States typically see with a simple "Mature" rating. Titles such as The Elder Scrolls V: Skyrim, Call of Duty: Modern Warfare 3, Dishonored, The Walking Dead, and many more. This means that these titles will not be allowed to be sold in the Windows 8 Marketplace.
But none of that really matters though since you can still buy these games through Steam, Origin, Green Man Gaming, and most every physical retail shop around.