Blizzard has Mac OS support, I don't see it being too much work for Linux native. The main problem is the massive amount of Linux distros. But they could support ubuntu and their offsets fairly easily.
I wonder how much Sam Lantinga is responsible for the existence. As far as I know he joined Blizzard after coming off of porting games to Linux at Loki Software. Interestingly, he's now at Valve.