Over on the Analog Science Fiction and Fact discussion board, Greg Ellis mentions the "egregious submission and contract terms" found in the role playing game industry. For example, if you plan to submit a story to the Amarillo Design Bureau, publisher of a number of games based around the Star Trek universe, you should first read this paragraph in their guidelines:
"All submissions of new material are accepted ONLY under the following terms unless specifically agreed otherwise in writing in advance by ADB: All materials submitted immediately become the property of Amarillo Design Bureau, Inc. and may be used, modified, expanded, or changed as ADB, Inc., in its sole judgment, sees fit. (It is not sufficient to claim an exemption to these rules within a submission; you must obtain an exemption first.) All materials used will be credited to the original author to the extent of his original submission. All claims of copyrights to material created from or for use with this product are invalid as they are 'derivative' copyrights requiring our permission."
Personally, I wouldn't submit to any place that had such a statement in their submission guidelines. But that said, I also understand their point of view. First off, they don't have to allow unsolicited submissions. Second, since these are submissions to an already created fantasy and SF world (and in the case of Star Trek, one of the most famous SF worlds in existance), it's more than likely that there will be similarities both among different submissions and with stories already being produced but not yet published. Finally, already created worlds like Star Trek are covered by copyright, meaning anyone wanting to write in that world has to abide by their rules (despite the wishes of the Organization for Transformative Works, which believes that fan fiction is transformative and legitimate, a view I don't agree with). As ADB's guidelines state, works written within these gaming world are "derivative" and based on my experience with copyright law that's something which might hold up in court.
When I worked as a senior editor at a book publisher, I saw cases where authors submitted very similar stories merely because they were working with specific guidelines within a particular fantasy world. This likely happens even more in the gaming industry and so they put this statement up to protect themselves. But again, I personally wouldn't submit to anywhere that had such a requirement. But since these fantasy gaming worlds are these companies own personal sandboxes, if a writer wants to play in them they have to abide by the companies' rules.