And having Steam on IOS / Mac is not promoting Steam enough, having people on the IOS (which most likely will be able to play HL3 as well) is good for their marketing. While nobody in the entire world which plays videogames will prefer a MAC over a PC to game on, there still are these bunch of groupies claiming that a MAC is actually useful for it, so valve just responds to that.
Linux is more useful for gaming than Mac will ever be. The devs just have to release it for Linux. Bring 'em on, the .deb packages!
I do hope that Steam will think about integrating with Wine. I'd hate the idea of running a second Steam in Wine just to play Windows games. Also, Linux finally has hybrid videocard support. Lesson learned: never buy a computer or laptop that says "Optimus Technology", "Hybrid Graphics", or "Intel Extreme HD", because it fucking sucks.
Yeah I guess maybe it's better that way to force devs to get off their lazy ass and replace DirectX modules by SDL modules, so it will work on Linux.