With the launch of the third edition of the popular game eight years ago, Wizards had sponsored an open licensing scheme. This license, called the Open Gaming License, or OGL, was a kind of open source license designed for game publishers. The result was an explosion of third party game companies supporting D&D and establishing their own game lines. Many of these companies became quite large and successful, notably Paizo Publishing, Green Ronin Publishing, and others.
Now, however, Wizards has stated that any company hoping to publish products for their new edition must agree to discontinue any currently open licensed products and produce no further open products at all — Dungeons & Dragons related or not. A number of companies had leveraged the OGL for their indepedent games, for example the pulp game Spirit of the Century.
In response to questions about this policy, Scott Rouse, D&D Brand Manager for Wizards of the Coast, says that "We have invested multiple 7 figures in the development of 4e so can you tell me why we would want publishers to support a system that we have moved away from?"
It seems to me that this is the equivalent of Microsoft telling people "If you want to make and sell software for Windows Vista, you can't make and sell any Linux/open source software!" Since this is a small niche market without the visibility of a Microsoft, this play to muscle out competition by making them choose "between us and open licensing" will probably succeed. Some other game companies are rebelling; Paizo Publsihing, for example, has declared their intent to move forward with the open-licensed previous version, essentially 'forking' the Dungeons & Dragons code base. But small gaming companies are small indeed, and Wizards of the Coast is owned by Hasbro (a recent development likely not unrelated to this change of heart)."