Comment by ptomato

Well, with OS X, at least, there is no retail Mac that meets the minimum hardware requirements previously announced, except possibly the Mac Pro (though it looks like even that benches lower than the minimum for the Rift). Given that and that Mac graphics driver/OpenGL performance lags significantly behind Windows, there's not really any reason to waste resources on the platform. I don't know what the current state is, but last I was aware, Linux OpenGL performance was also significantly worse than on Windows, so it seems pretty reasonable to me to leave it out as well.