Do they meant "greatest" in that its a fun, kooky, place for developers to work? Because in that sense, I could see SEGA not being on the list. They've released awesome games in 2012, but for the staff and dev teams it wasn't all that fun.
But if they're going by the output, then I think SEGA should be on the list. I mean, I like Halfbrick but c'mon. They released one iOS game in 2012, thats it: Jetpack Joyride. It's a fun title for the platform, but I really can't agree that a place like Halfbrick is greater than all of SEGA, or even internal SEGA devs like Creative Assembly or SEGA hired teams like Sumo Digital. I'd think Sumo and CA totally deserve spots on that list.