What he's saying is that Steam will use the Linux kernel, but the UI that runs on top of that will probably not be a geek paradise.
And what I'm saying is that if the kernel is Linux (really who cares about pedantic details like whether it is a kernel or an OS... I mean, really?), that it can't run all the existing Steam Windows games natively and hence you are limited. Unless all those games magically get ported to Linux.
There's probably an awful lot of Linux running in your house that you don't even know about.
Or care about. Which was one of my previous points. The only places Linux gets some success in the consumer market is when the OS is nicely hidden away and end users don't need to interact with it directly. No-one goes to Frys and buys a router because it runs Linux. No-one cares.
Look Linux is fine, I even develop and debug on both Linux and Windows at work (although by far I prefer to develop on/for Windows). But there are cases where it just doesn't make sense and trying to create essentially what is a gaming PC using Linux just isn't going to be a success.
And no-one has answered my question as to what makes a Linux based "SteamBox" better than say any one of the available pre-built, living-room friendly gaming PCs running Windows and Steam? Hmmm?