Well given (a) Valve's distaste for Microsoft's strategy and (b) their anyways insane profitability per employee I could see them at least releasing a title a few weeks earlier on linux and OSX than on Windows.
Valve's problem with Windows is that they perceive them to be going after a more closed system. Snubbing Windows for the far more closed OSX would be ridiculous, so that's never going to happen. The Linux market for games is absolutely tiny compared with Windows, so there's no way they are going to release a major title on Linux first either.
Valve's problem with Windows 8 is the Live Store, and Metro interface. Specifically the fact that the Live Store is the only way Microsoft will allow applications to be distributed to Metro interface, with the revenue cut that Microsoft want.
OS X is not "far more closed". Darwin, the UNIX kernel and utils that OS X runs on top of is fully free and open-source. It's just the Apple-specific APIs like Cocoa, Carbon, Quartz, Aqua and all that jazz that is closed-source and proprietary.
Can I get source access to the NT kernel on Windows? Nope. That's Microsoft's secret and novel invention that is supposedly the best OS in the world, so they have to keep it on lockdown. </s>
Just being restrictive of what computers can run your OS does not make it closed. When has Microha$h ever supported FOSS? Think about it for a second.
Good luck building them. Many of the code dumps are incomplete (like dyld and ld64). They reference private apple headers and won't build without them. Granted, they can probably be hacked to build in some cases and having the source just for reading is still nice.
With launch screen, you mean the new Start screen? All Start menu shortcuts automatically appear there (except if they appear to be uninstallers and such, but those are still searchable and can be added manually). So if you tell Steam to create Start menu shortcuts for a game, they automatically appear on the Start screen.
If Steam can still trivially get its third-party-bought programs onto the metro-styled start screen, the popular reporting on that situation was off.
And I can't even find a story where Gabe himself actually expresses an opinion on, or concern about, the MS App Store. His comments seem to entirely revolve around Metro being bad for desktop usability and Windows 8 not selling. So the popular reporting that Gabe was specifically upset about the store (via it's limitations) seems to have all been bullshit/editorial.
Upon digging deeper, it seems his concerns about Windows 8 aren't materially different than his comments about Vista (via complaints about DX10 being Vista-only, as Vista wasn't selling).
If it were about the app store, why does Gabe have nothing to say about the Mac App Store?
In my poking around on this, I saw plenty of assertions that this was all about the app store, but nothing is ever attributed to Newell except his lament that the usability is off and the sales aren't there.
Because Mac and iOS gaming doesn't represent such a large share of their business. The doom and gloom doesn't make sense otherwise, Steam functions perfectly well on Windows 8, as do all other desktop, non-"Modern UI" apps, so there's no other conceivable reason for him to get irate.
> "The doom and gloom doesn't make sense otherwise"
But the 'doom and gloom', from Gabe's mouth, doesn't seem to be any more extreme than his stated position on DX10/Vista. As far as I can find, the press are the ones taking his comments to extremes, reading into them about app stores, etc.
Seems like wishful thinking. If there was going to be any snubbing, I would expect it to be an early release for the PS3 or some other platform that would make Valve money. Even during the heyday of Linux ports in the 90s, from Quake 3 to SimCity 3000, Linux on the desktop never took off.
I could see a world where they HL3 is exclusive to the Steambox (or whatever it's called) for a period of time. Alternatively, they could offer lower prices (or subscription things) to make obtaining valve games significantly cheaper/easier on their own hardware.
I think they have to move quickly though - the steam-sale model is getting copied by other PC download services and they stand the chance of getting lost in the crowd.