Well, just in case some couldn't read into what Carmack was saying a few years ago about iD's hesitation about bringing out Rage for linux (as if the parting of ways with TTimo wasn't clear enough), it was spelled out in Quakecon's keynote.
A new public enemy number one? First Epic and now Carmack. Hope Valve is successful with Steam.Linux development is another story altogether. Even though Valve is now actively pursuing the Linux market, iD has been there before, and just has not seen positive results. Remember how many past titles from iD actually ran on Linux, and for how long these were supported? John says that Linux development simply does not pay the bills. It creates goodwill among the Linux crowd, but that is about it.