cw8: I have the boxed version of Superbox and steering it clear off Steam, I also have the Steam version of Superbox which I'm using to get AP.
Sadly, they have not confirmed atm that the box version will not have Steam, yet. There's a chance the box version has Steam. Even though I'm getting it free on Steam, I have all intention to get the box version if it doesn't come with Steam, however if Steam is mandatory with the box version I guess I'm not getting anymore.
Yes, would be interesting to know if it's a steamworks game or just a pr-move (earlier release, free). They only say it's an add-on and you need the original game installed. I really hope it's just pr with the goal that many from the community want to play it now, create an account on steam and activate their superbox. Otherwise I don't see a reason why the new add-on should be free and released two month before the disc version.