Valve doesn't build the hardware. They merely developed the spec. In publishing the spec for some reason Valve originally left mention AMD CPUs, APUs and GPUs out of the documentation. AMD whined. Valve sighed. Then Valve updated the document to say "just because we didn't mention AMD chips doesn't mean you can't build a Steam Box using them".
Then this news goes up the butt of an AMD fantard, and comes out his mouth garbled into: "Valve building AMD-based Steam boxes!"
The desperation is palpable. The reference designs demoed bu Valve have been all Intel and nVidia, in keeping with the originally published specification. OEMs who build Steam box devices can use whatever they want as long as the combination meets the performance requirements.
In other news, did you see that Intel grew cloud/data center business 12% in one single quarter? Did you see the upgrade? Amazing. AMD talks about cloud, but continues to lose share and revenues in server CPUs, and Intel says very little and grows its business a half billion dollars in a single quarter.