I watched an interview with Ryan Dancey, architect of the Open Gaming License, in which he discussed what is copyrightable and what is not. His example, though, was the combat tables in AD&D (1st edition, naturally), which he claimed were not made according to a formula, but were instead adjusted by Gary Gygax manually according to "what looked good", and were therefore art and copyrightable. That, though, is not the case at all. All of the combat tables in AD&D (and the "alternative combat system" in the original D&D booklets) were simply a highly "at the table" usable expression of a fairly complicated, but still systematic, formula. This can be attested to by the existence of THAC0 ("To Hit Armor Class 0") in the listing of monsters in the 1st edition Dungeon Masters Guide. There was also an "AL", standing for "Attack Level", listed in the Monster & Treasure Assortment, Sets One-Three: Levels One-Nine, which is effectively a "To Hit Armor Class 9" (where Armor Class 9 represented an unarmored target) entry. Dancey is simply confused by what he thinks his team was able to add to the D&D legacy in terms of rules systems.
Anyway, that's just a thing that I felt I had to get out there.