At a certain point, it's up to the users to show up.
I think that's what sinks OS X support. [1] And that's the big, recurring question-mark with gaming on Linux.
The vocal subgroup asks and cajoles and begs. But those devs who make the effort don't seem to find a large enough market to justify it.
[1] It didn't help that Apple's Mac App Store arrived so soon after OS X Steam showed up. Nor that mobile computing got so large to the point that PC upgrades basically stalled.
Another thing to consider about Mac gaming: since iMacs and MacBooks are essentially un-upgradable and they're not particularly designed for gaming in mind, they tend to age faster than a similarly-priced self-built tower PC (at least for gaming.)
I don't think that's going to be an issue for Linux enthusiasts, but it will be an issue for this "magic grapefruit" they're talking about.
I seem to recall gabeN posting to the effect that the average Mac running Steam was better-equipped than the average PC running Steam. If that's true, the non-upgradability might not have entered into it.
As to this "piston" thing here - I don't think upgradability will be an anchor. The whole project isn't remotely feasible unless a distro for build-your-own boxes is also launched. In which case the specifics of this box are more a blueprint for builders and a performance baseline for developers.
Sales probably wouldn't even track net adoption until the enthusiasts build out their custom rigs and start convincing their less-technical friends they can have almost all the same awesome without getting any thermal paste on their hands.
The vocal subgroup asks and cajoles and begs. But those devs who make the effort don't seem to find a large enough market to justify it.
[1] It didn't help that Apple's Mac App Store arrived so soon after OS X Steam showed up. Nor that mobile computing got so large to the point that PC upgrades basically stalled.