Sure it does. Catering to the Linux community creates good will. The geeks that use Linux often have influence over the technology selections of others and are more likely to recommend products from a company that, in their eyes, has done something good. Every business decision does not have to equal measurable profits. Some decisions may have no effect on the bottom line today, but by doing The Right Thing by some, will reap rewards in the future.
... Or maybe Carmack just wants to play a little FFA on his Linux box. :)