Let me tell you what is going to happen.
The television itself will be designed by Apple to allow for everything to be done without having to have lots of other boxes connected and sitting underneath. Tv programmes, films and music will be available in a similar way to the Apple TV device, albeit improved.
With regards to gaming, they will allow access to the app store via the tv, with existing applications able to run as is. This will form the the part of the gaming experience handled directly by Apple, nothing more. You will, of course, need to purchase an iPhone, iPod touch or iPad and link it up to be able the play the games as the primary tv interface will be using Siri.
Where valve will be involved is in the form of a 'premium' games provider, accessible as an application like any other. They will allow people to play more traditional games via steam but allowing it will be the extent of Apples involvement. They will also allow valve to link up a more traditional controller to play these games, but this will be designed and sold by valve, not apple.