Heather Grove Copyright works a bit differently in the roleplaying industry than in most others. If the authors each held the copyright to their own work, then every time an RPG book came out, the RPG company would probably have to go back, try to figure out what material that book built on, and get permission from each author of each of those books to put out the next one. The company would have to get permission any time it wanted to do anything like revised editions. Even more importantly, most RPG work is done at the instigation of the companies. They came up with the basic ideas and then farmed those ideas out to the authors to be developed - it's very rare these days for companies to accept outside proposals.
Most companies have their books planned a year or three in advance.
So it seems a bit odd that the author would hold the copyright when someone at the company came up with a number of the ideas. This further complicates the copyright matter. Add on top of this the fact that it would be inappropriate for the author to re-sell the material to anyone else, which he could if he owned the copyright. Gaming material is part of a company's proprietary world, which they have spent a great deal of time and money developing. They mean that the company owns the work you made, and can do anything they want with it.