Publishers advertise, create the box, dvd, manual, and ship them to walmart? is that it? I'm also surprise they chose SquareEnix instead of stardock.
Another thing publishers often do is supply the developers with an advance, bankrolling the development. Also they often perform the market research, and then provide feedback to the developers (or just forcing it upon them
) in order to try and make the game sell more. The role of the publisher can vary, and depends on the specific publisher and relationship\agreement between the publisher and the developer.
Read a point made by someone somewhere else that reminded me that Sega were the ones who published Space Siege, so perhaps this move isn't as odd as first thought. Guess GPG must look really attractive to Japanese publishers.