Here's Microsoft doing what they do best: Not pleasing their users.
According to a report from GI.biz, Microsoft will not allow 16+ rated games (this includes 18+ games) on the Windows 8 digital marketplace in Europe. The same goes for the US, where content rated Mature isn't allowed to be sold through the marketplace either. Bravo.
The report is based Casey Muratori's rather extensive article about Microsoft and Windows 8, and how Microsoft is doing everything wrong with their closed distribution model.
"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," wrote Muratori.
It is, however, still possible to run 16+/18+/Mature content on a computer with Windows 8, but developers will not be able to release their content on the Windows 8 marketplace.
Some of the games that have recently received a PEGI rating of 18+ in Europe are Dishonored, The Walking Dead and Skyrim. Sounds like the Windows 8 marketplace won't have a lot of success with future games, then.