Let's just call them "Living Room PCs"
I love the name Steam Machine. It is elegant and alliterative. It is the trademark for Valve's initiative to push PC gaming into the living room, which I fully support. All "Steam Machine" really means though, is that the retailer has paid licensing fees to pre-install either SteamOS or the free-to-anyone Steam client onto a normal desktop PC.
I applaud the manufacturers who are pushing performance in small form factors. That kind of innovation is what the PC market really needs right now. It is something I am trying to do with my custom PC designs.
Some retailers don't get it though. The whole idea is to compete with consoles, so it is rather pointless to market $2-3,000 high-end rigs as Steam Machines. There is a lot of overkill in the hardware too. These devices are going to be connected to 1080p HDTVs. That means that they really don't need more than a GTX 760, maybe a 770, to max out detail settings in all but the most masochistic games (*cough* Crysis 3 *cough*). It is absurd to offer Steam Machines with GTX 780 TItans or dual GPU solutions. Yes, 4k displays will be affordable within a couple of years, but even today's $700 GPU doesn't guarantee you'll be able to crank up the details at 4k.
The biggest problem is that SteamOS simply cannot replace Windows the way Valve wants it to. The only place it conceivably can is in tiny NUC devices which are limited by their CPU's on board graphics anyways. Anyone shelling out for a discrete GPU is going to want to play games that require DirectX, and probably wants to use their $1000+ PC for more than just home entertainment. This is especially true when you get in to $2k machines where you can't even use the extra power unless you are doing multiple displays and/or professional graphics/video work. If you look at what these outfits are offering, most of them either dual boot, or simply have the Steam client pre-installed.
So let's just call these devices what they are, Living Room PCs. LRPC is simply the evolution of the HTPC as miniaturization allows small form factor PCs to offer desktop class performance. I love what Valve is trying to do, but paying them to use their branding and have their free software pre-installed is not what should define a whole class of device.