Valve clarified that publishers and developers are no longer allowed to promote other platforms for their games on Steam. This includes store pages and communities.
The clarification can be found here.
This news comes as some publishers have used Steam as a way for them to promote other versions of the game that they are offering. As you can see in the FAQ section of the link above, the question reads, "Can I use the Steam community to let customers know of non-Steam versions of my game?"
The response reads "In the game you ship via Steam, and in communications on Steam, you may only promote the Steam version and its availability via Steam, and not other distribution outlets. This applies both to full versions of your game and to content patches that change the existing version."
So, not only does this cover the full game, but any content patches, bundles, or anything else that will technically add things to the game.
I believe this is a fair limitation, and although it may hit publishers/developers a little bit, I am sure they will find other ways to promote their games for different distribution platforms.