We had a Linux version early on for compatiability purposes, but have no plans to make the final game for Linux.
but if it comes to online gaming most money comes from monthly account fees, not from the actual game sales.
i can think of one huge advantage of linux based game - you can box it together with an operating system :]
think about it - if there was a linux edition of e.g. world of warcraft or warcraft 3 with a linux (e.g ubuntu) install cd in the box, or even blizzard's dedicated distro. wouldn't that be cool?