The recently unveiled Windows 8 Marketplace regulations state that games rated above ESRB Mature and/or PEGI 16 won't be sold through the online store in USA and/or Europe respectively.
While most blockbuster games in USA fall within the ESRB Mature rating, it is interesting to note that a lot of those games are rated PEGI 18+ in Europe.
But that is not the only problem. Careful inspection of the Marketplace regulations reveals that hosted apps "must not contain content or functionality that encourages, facilitates, or glamorizes illegal activity." Said apps also "must not contain content that encourages, facilitates or glamorizes excessive or irresponsible use of alcohol or tobacco products, drugs or weapons."
Windows 8 Marketplace is the only way for Windows 8 users to get programs that take advantage of the operating system’s new interface and features. Users are still able to get classic windows applications through other venues though.
Between GTA that encourages car theft and prostitutes’ manslaughter to Borderlands which glamorizes weapons, it seems that Windows 8 Marketplace will be limited to selling annual FIFA releases and Spongebob SquarePants games.