In theory, I fully agree, but so far, no one has really explained why this is going to sell. That post people praised was discussing why it's good for Valve, I don't think anyone couldn't see why this would be good for Valve, but why is a gamer going to buy it?
There are three 'SteamBoxes', there's the low level $100 (not an exact number, just Gabe's estimate a few months ago) streaming machine. This is the only one I think anyone can make a real use case for. You have a gaming PC in your den, and you want to play a controller friendly game on your nice big TV. It won't feel as good, or look as crisp as playing on your gaming monitor, and $100 is far far more than a HDMI cable that would do this much better, but some people don't want to, or can't disturb their walls with new cables, or various other reasons that someone would do this. It's bad, but it makes sense for a number of users.
The second SteamBox is the 'console' spec version. This doesn't make sense to me. Gabe claims they can match performance and price with consoles. This is logically not the case, because consoles are sold at a loss at launch, and they're manufactured in far greater numbers than a SteamBox will be, and they get better performance with their spec than a similar spec PC. But let's say none of that is true, and they can match PS4 perfectly with performance and cost, why would someone buy it? People who have never bought a console haven't heard of Valve. Valve fans have gaming PCs already, and they could buy a console and get the exclusive games for it, a SteamBox gets you no exclusive games (and if it did, people would lose their shit).
The third SteamBox is a full priced gaming PC, this is the most pointless of all. Buy a second full priced gaming PC to put under your TV. Almost no one would do that.
Of course Valve want to break away from Windows, but why do the users?