The "closed" part of the ecosystem is Windows RT, in the sense that apps for that platform must come from the Windows Store. Windows 8 runs Steam very well, and has no such restrictions. Steam's not available on the iPad either.
I understand why. The biggest problem of the convential desktop is the ugly compomize between freedom, power users and professionals on one end, and casual consumer usage at the other end.
But that does mean, many of Valves current customers, that buy midrange devices, will end up on RT or iOS.
And the crowd on this site, will likely find the devices aimed for them moving to a more expensive and exclusive niche.
Your argument is completely fallacious.
Amazon sells a Mac Mini for 600EUR (at least Amazon.fr does). That's about what an unsubsidized iPhone costs, right?
So where is this doom-and-gloom everything-is-locked-down-except-the-ultra-expensive actually coming from?
Do you want an iPad/iPhone/WinRT/Android tablet with "apps", or do you want an x86 device with the ability to run whatever binary code you want and an OS that enables that.
It's not about price, because you're right, I can find devices in both categories at literally all sorts of data points. But it is about the experience.
Valve's business RELIES on the experience that enables users to run, in this case, native code. Since they're being pushed out as a result of this shift... they're naturally trying to warn people and shift interest to a platform where they can more easily operate... or survive.
In fact, your example is ironic. People are more likely to go buy a $500 iPad than they are a $300 full featured Windows laptop. That's exactly what worries Valve. Or it should.
The article speculates that the emergence of Windows Store app platform from the Windows desktop could become similar to the emergence of Windows from DOS, and that newer technologies will similarly only be available on the Windows Store app platform.
It describes the locked-down properties of the Windows Store, and, extrapolating from the current certification requirements for Windows Store apps, it asserts that a game like Skyrim would be denied certification on Windows Store in 2032 because of its PEGI rating.