I found this article thrilling, as I am an author that has written a clone game, called Mazes & Perils, which will for sale starting tomorrow on RPGNOW.com for only $1 for the opening weekend.
The argument has been thrown around a lot in the gaming community that clones are not legal, and some argue back saying you can't copy right "system mechanics".
Well, the argument is basically settled in my opinion, as now we have a court case ruling in favor of the clone writers, saying there is no protection under US copyright law! Here's a direct quote from the article:
If you are interested in reading the backstory on this case and what happened, I've included the link below for you reading enjoyment!"In no case does copyright protection for an original work of authorship extend to any idea, procedure, process, system, method of operation, concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in such work."
Reference Link: http://www.strebecklaw.com/court-rules-favor-cloned-tabletop-game-no-protection-us-copyright-law/