3D Realms has shut down development of an amateur mod for Half-Life 2 which was meant to recreate Duke Nukem 3D. 3D Realms, which developed the classic Duke Nukem 3D, is currently working on that game's sequel. There is clearly a tension between protecting intellectual property and promoting the game. In this case, 3D Realms made the safe bet.
Coverage at http://shorl.com/hepypugrostubro