If Miscrosoft goes full-on walled garden it'll be interesting to see what tries to take it's place.
It'll never happen on the desktop. Phones and tablets are another matter, but nothing's really in a position to take their place unless people start buying them first.
I'm going to go with "I thought the app store and stuff was just a level on top of the regular Windows and you can revert to a traditional desktop environment if you want."
Yes and no.
Nope. Start Menu is entirely gone, "Desktop" is just an app within the Start Screen that is your new homescreen.
This much is true.
That Ars beta review I linked/quoted at the top of the page is instructive; you can't get around the Start screen but they said you can avoid most of the rest of the Metro dickery. On the whole they seemed to think it was actually pretty good but with some rough edges.
But that's a bit of a tangent, really. Yes, the standard version of Win8 is still an open platform; yes, you can install arbitrary apps; no, the App Store doesn't PRECLUDE the use of Steam or any other way of getting games.
But this is goddamn Microsoft we're talking about, remember?
They've already been strongarming publishers into following their checklist to get the GFW logo.
This is going to be more of that, coupled with good old-fashioned 1990's-vintage "it's what's on my desktop so that's what I use" ubiquity.
Now, I don't see Steam taking nearly the kind of hit that Netscape did; Valve's in a much better position now than Netscape was back then. And EA's got enough money to keep throwing at Origin that it'll be around for years even if nobody's that damn interested in actually using it. So we've got a much healthier competetive market now than we did 15 years ago (plus an EU ready to pounce on absolutely anything MS does, but I don't think that's likely to affect their stateside operations much. Or their European operations.). It's not going to be the catastrophe that we saw during Browser War I.
But it IS going to hurt Steam, and I think it's going to hurt indie devs (since they'll now be faced with an App Store that gives them more exposure but eats a greater percentage of their profits).
But honest to God, if it makes Linux a more attractive platform both for gaming AND for general-purpose computing, I'm not gonna lie, I am skeptical at the prospect but it would make me pretty goddamn happy if it happened.
The rub is that Win8 is actually going to make it HARDER to install Linux. See, MS is pushing for all vendors, going forward, to support a firmware-level authentication scheme that verifies binary signing at an OS level -- basically, if your OS doesn't authenticate, it won't boot. It's a security feature, but it has serious ramifications for Linux-based OS's.
Hopefully, most hardware vendors will allow users to disable the feature. And some Linux distros -- including Ubuntu, the biggest one (and the one Valve is officially supporting, so far) -- ARE signing their bootloaders. But I think we are very likely to see certain hardware models that will not support arbitrary OS installation.