Mentioned this week by one of the Mac Tech Support MVPs in this Battle.net thread was this comment: "Last time I checked the developers have their own internal build of a linux client they use for testing."
This comment came after another World of Warcraft MVP had mentioned:
One of the big problems with Linux, and this is from other game developers too, is the problem of targeting a specific version of the platform. Since everyone is free to create their own distros, they can become somewhat unstandardized. That makes "targeting linux" difficult.
Add on that there are far fewer linux users than windows/mac users, and that you can play wow on linux using Wine... and there isn't a lot of reason to target even a specific distro.
Unfortunately for the Linux gamers out there, it doesn't look like the tide is turning yet inside Blizzard.