I'm reminded of Valve talking about supporting Linux for their half-life2 engine. Their experience was that they were able to find some fabulous engine speed up improvements that they then backported to the windows version.
The common thread with supporting Linux seems to be that it's not necessarily worth it from a revenue/market size point of view, but there are all kinds of intangibles that you only get by doing cross platform development.
At the coprorate level, intangibles don't help you move up the chain, unforuntately. I imaigne there are many well-intentioned devs that lack the choice to keep working on these things, or have to make other choices in the grand scheme of things.
The common thread with supporting Linux seems to be that it's not necessarily worth it from a revenue/market size point of view, but there are all kinds of intangibles that you only get by doing cross platform development.