Steam Machines aren't available on walmart.com. The Alienware Alpha is available, but that isn't a Steam Machine (although it's the same hardware as the Alienware Steam Machine). Several ZOTAC ZBOX mini PCs are offered by third-party retailers on walmart.com, but not the ZOTAC NEN SN970 Steam Machine. I'm not certain brick-and-mortar Walmart stores would carry Steam Machines if Walmart doesn't sell them online.

The GPU in the Alienware Alpha and the Alienware Steam Machine (it's the same hardware) is a "customized" GeForce GTX 860M: http://www.eurogamer.net/articles/digitalfoundry-2015-alienware-alpha-review.

The ZOTAC NEN SN970's GPU was still advertised as a GeForce GTX 970M as recently as September of this year: https://web.archive.org/web/20150909201038/http://store.steampowered.com/app/353530/. It is much more likely that the 970M GPU was rebadged for prebuilt use as a GeForce GTX 960 than it is that it was replaced by another GPU in the intervening timespan between early September and the November 10 launch. http://hexus.net/tech/news/systems/87776-zotac-nen-the-powerful-small-form-steam-machine/

It makes sense that mobile GPUs would be used in the Alienware Steam Machine and the ZOTAC NEN, given the form factors.

Of the 10 manufacturers listed at http://store.steampowered.com/search/#category1=993, all but 3 (Dell/Alienware, ZOTAC, CyberPowerPC/Syber Gaming) use non-custom cases and components.

ALTERNATE's Steam Machine shown at https://www.alternate.de/html/theme/9335 uses SilverStone's RVZ01 case.

Digital Storm's Eclipse Steam Machine shown at http://store.steampowered.com/app/353430/?snr=1_7_7_230_150_1 uses SilverStone's RVZ01 case.

MAINGEAR's DRIFT Steam Machine shown at https://www.maingear.com/custom/sff/steamos/index.php uses SilverStone's FTZ01 case.

Material.net's Steam Machine shown at http://www.materiel.net/ordinateur/materiel-net-steam-machine-haswell-pc-gamer-99543.html uses Fractal Design's Node 304 case.

Next's NextBox Steam Machine shown at http://nextbox.nexths.it/ uses Cooler Master's Elite 110 case.

Scan's/3XS Systems' Steam Machines listed at http://www.scan.co.uk/3xs/custom/gaming/steam-machines offer a choice from among the following cases: CiT's S013B, Fractal Design's Node 202, SilverStone's RVZ01, and SilverStone's RVZ02.

Webhallen.com's Steam Machine shown at http://store.steampowered.com/app/353520/?snr=1_7_7_230_150_1 uses BitFenix's Pandora Core case.

Anyone can go buy any of these cases and build their own systems, with standard desktop graphics cards. PCPartPicker is a resource available if needed (and I can often find better prices than PCPartPicker lists).

As for the Syber Steam Machine, while the case is unique to CyberPowerPC/Syber, the internal components are not custom.

The Alienware Steam Machine and ZOTAC NEN SN970 Steam Machine have custom cases, and use nonstandard (if you want to call it that) GPUs. The Alienware uses an NVIDIA GeForce GTX 860M GPU that is soldered to the motherboard. The ZOTAC NEN SN970 uses an NVIDIA GeForce 970M which has been rebadged as a GTX 960 (case in point, the GPU in the NEN is advertised as having 3 GB of memory, but a GeForce GTX 960 in actuality comes with either 2 GB or 4 GB of memory, whereas the GeForce GTX 970M comes in 3 GB and 6 GB configurations, and the NEN was originally advertised as including a GeForce GTX 970M).

If I wanted a Steam Machine with console-like dimensions and aesthetics, I would get the NEN, but not at $899.99. The Alienware Steam Machine is gaudy, although undoubtedly there are people that would appeal to.

IMO, it really should be Valve promoting the Steam Machine brand, as it is Valve's brand; the hardware manufacturers are merely licensees of the brand. The manufacturers are already operating at thin margins on the Steam Machines when you take their costs (such as labor, equipment, insurance, utilities, etc) into consideration. Valve receives 30% of the revenue for every game sold on Steam and an undisclosed chunk of the 75% it appropriates from mod sales, surely it could invest a little of that in promotion of the Steam Machine brand? Valve's current approach reminds me a lot of https://en.wikipedia.org/wiki/Apple_Pippin#Marketing_failure

A brick-and-mortar Best Buy? I ask because there are no Steam Machines listed on bestbuy.com, only the Alienware Alpha (which is not a Steam Machine, despite having identical hardware configurations to the Alienware Steam Machine), the Syber Vapor (which should also not be confused with its Steam Machine cousin), and a few ZOTAC ZBOX mini PCs (but not the ZOTAC NEN SN970 Steam Machine). The Vapor and one of the ZBOX models are available from Best Buy, and the Alpha is only available through the third-party marketplace, with no in-store availability for the Alpha listed for Los Angeles, New York or Chicago. Frys.com also doesn't carry Steam Machines, though several Alpha models and a ZBOX are available.