The reason Steam and Valve are focusing on making a more console friendly setup boils down to simple statistics. If you sit down at your PC and play a game the most you'll play it for is about an hour (on average.) If you sit down on your couch and play a console game, it's been shown that you will invest at least 2 hours into your game, if not more.
The longer you have a gamer's attention, the more likely you are to make money off of them.
I'd like to see more of those statistics, to see if there is any unintentional/intentional bias due to PCs being more than a gaming device. Consoles, after all, have almost no use except games, so if you sit down at one, that is what you are going to do with them, and that is the condition when you sit down. The same or similar conditions will exist with a dedicated Steam Machine.
Not trying to start an argument with you, in the least. When I first saw those same statistics a few days ago, I thought the same thing I just said above.
Edit: By the way, I noticed this interesting wording:
Can I use a controller if I don’t have a Steam machine?
Yes. It’ll work very well with any version of Steam.
It says it works with Steam, not computers. Makes me wonder if its design is unique enough that drivers do not exist for it to work with a computer directly, and requires Steam to aid in the input-processing.