http://www.computerhistory.org/atchm/macpaint-and-quickdraw-...
Carmack released the Quake1 and QuakeWorld sources, and I think also q2 and q3 eventually too.
StarCraft is ancient and the source is of no commercial value to them any longer. They don't benefit from its secrecy, but we do benefit from its release.
Then again, this is the company that sued open source developers who re-implemented a server (bnetd) for one of their proprietary protocols. It was that day I resolved to never give them money again.