No, there's actually a fully-supported Mac version. I've never tried it but Blizzard is very good about supporting Macs so I would assume it's on par with the Windows version.
Blizzard is the best Mac game developer. I don't have SC2, but WoW works exactly the same on a Mac as it does on a PC, and patches, xpacs, etc all come out on the same day for both systems.
