Valve has performed without making much noise a policy change in your FAQ About Community Centers on Steamworks, Steam’s portal for developers. In this FAQ it was asked if the studios can make other versions of their games known to their Steam community and the answer has been clear, this will no longer be possible.

“In the game that is shipped through Steam, and in communications on Steam, you can only promote the Steam version and its availability through Steam, and not other distribution points. This applies to both full versions of your game as well as content patches that change the existing version. “

Community hubs on Steam include discussion boards, multiple pages to display screenshots, and artwork, but also a news board. The vast majority of publishers and developers are using this bulletin board to advertise your games on other platforms (either for being a new release, offers, etc), which would now be prohibited under these new rules.

It is unclear when the new rule was added or how Valve intends to ensure developers adhere to it in the future.

via: Gamesindustry