I'm no expert in this subject, but mxyzplk has written a good summary of the issues affecting open gaming and the upcoming release of 4th Edition D&D. The open licensing associated with the 3rd Edition spawned a number of successful 3rd parties and add-ons that made the system far greater than it might have been otherwise. I've attached his writeup on the subject below, and you should really read it if you are interested in D&D, Gaming, or trying to apply 'Open' licenses to things besides code.

In January we had the chance to ask the designers of Dungeons and Dragons Fourth Edition a few questions about the new version of the classic tabletop game. The Wizards of the Coast Community Manager, Mike "Gamer_Zer0" Lescault put our questions to members of the development team, including: Andrew Collins, Chris Perkins, Scott Rouse, and Sara Girard. Some of the questions weren't quite answered in as much detail as I would have liked. That said, they've given us a great opportunity to follow up on their responses. If you have a follow-up question, put it in a comment below (one question per comment please). We'll pass on five of the best, and the designers will answer your question on-camera at the Dungeons and Dragons Experience at the end of this month. We'll post the video to the site early in March. This is a great chance to put a face to some legendary designer names, and get your unanswered issues resolved. Get asking.