Entertainment is not a one-size-fits-all world. We want you to be able to choose the hardware that makes sense for you, so we are working with multiple partners to bring a variety of Steam gaming machines to market during 2014, all of them running SteamOS.
Where Sony and Microsoft follow the iOS model for consoles, Valve is aiming for the Android model, including Valve's own line of 'Nexus' devices. As Valves notes, no restrictions - you can change the hardware, software, and install any operating system you want. The right approach, obviously.
The cooperation between Valve and NVIDIA is quite close, as NVIDIA details on its blog:
Engineers from Valve and NVIDIA have spent a lot of time collaborating on a common goal for SteamOS: to deliver an open-platform gaming experience with superior performance and uncompromising visuals directly on the big screen.
NVIDIA engineers embedded at Valve collaborated on improving driver performance for OpenGL; optimizing performance on NVIDIA GPUs; and helping to port Valve's award-winning content library to SteamOS; and tuning SteamOS to lower latency, or lag, between the controller and onscreen action.
This is going to be big. After being defeated in mobile, it seems Microsoft is facing another frontal assault on another one of its strongholds: gaming, whether it be Windows or Xbox.