Well that blew up, huh? If you follow emulation or just gaming on the whole, you've probably heard about the controversy around the Dolphin Steam release and the Wii Common Key. There's been a lot of conclusions made, and while we've wanted to defend ourselves, we thought it would be prudent to contact lawyers first to make sure that our understanding of the situation was legally sound. That took some time, which was frustrating to ourselves and to our users, but now we are educated and ready to give an informed response.

TL;DR: The Dolphin team got legal counsel and are confident that they are not in violation of either the DMCA's anti-circumvention provisions or copyright law, but since Valve has final say over what gets published on their platform the team is abandoning efforts to release the emulator on Steam. However, some of the features intended for the Steam build (including a Big Picture mode) will still be developed and introduced to the mainline Dolphin builds.