Theres a lot of material in the SRD that seems too simple to copyright or comes from the public domain. Why does Wizards of the Coast call the whole thing Open Game Content (OGL)?
One of the objectives of the OGL/d20 project is to create a “safe harbor” that clearly identifies material that can be used, derived from, modified, and distributed without fear of litigation. To that end, the SRD contains material that is public domain, copyright, and somewhere in between. But using the OGL, it all carries with it the same, uniform set of rights, thus creating the safe harbor.
