I had to download the demo and see if it was indeed using GPAA. I took a PIX capture of it, and unfortunately I see no evidence of GPAA being applied. Without FSAA enabled in the menu everything looks jagged. With it enabled there's some sort of crude "Edge AA" effect applied, but this is done through a fullscreen pass. In the frames I captured the game never drew a single line primitive. If the game is indeed using it, and that option is not just a remnant from some prototyping, then I suppose it's only used for some specific geometry somewhere.