Just imagine the effect an exclusive linux release of HL (ep?) 3 would have. If Valve really wanted to piss on Microsoft's foot, that's what they should do.
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.
Steve Jobs proudly described the Mac as closed as opposed to Windows "open and fragmented" approach.
OS X is specifically designed not to work non-Apple hardware, even hardware that is perfectly capable of running it.
Parts of it are open source, mostly because those parts were an extention of existing open source software.
"OSX" is not free in any sense of the word.
Microsoft are still a far cry from the likes of GNU/Linux in terms of openness, but almost nobody would describe the Mac platform as "more open" than Windows.
It's all about Microsoft's rule that you can't put anything on the "Metro" launch screen unless it's installed from the Microsoft App Store.
Which means Steam and all its titles would have to be launched by explicitly navigating to the classic desktop. Which is beyond Apple's simply providing a parallel way to get software onto OSX.
If Apple didn't allow icons in the Dock, unless the app came from the Mac App Store, I'm sure you'd see a similar reaction from third-party platform creators like Valve.
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.
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.