Ok, I am not a lawyer, but i have done research on this subject. Patents apply to inventions and copyright to artistic expression the artwork and the product identity material (such as the named Greyhawk spells, gods, monsters etc in 3.5). Trademarks are logos, brand names and other owned names that are designated as a trademark or registered as a trademark. Dungeons and Dragons and WOTC's logos are trademarks.
First off, a patent has to add three distinct and new improvements to an existing invention to be approved as a patent. Magic got its patent because it added value to card games. 1) It was collectible and players built their decks from a supply of cards that is different from other players. 2) It had tapping to show resource use. 3) It had a mana pool, giving the game an intangible resource each player generates and uses.
Because of these three differences from all pre-existing card games, Magic got its patent. If a card game uses these features together, Wizards can technically sue them for the life of the patent. This is not always in wizard's best interest. Often games come along and violate the patent (Spoils being one of them). But it is not worth it to wizards to go after them because they do not threaten Magic's throne.
Star Wars (from Decipher) is a good example of a game that purpose built its self with the patent in mind. It could use 2 but not all 3 of the features. So, a game can come non-random and have tapping and build your deck from a assortment of cards and a "mana" pool. It could have random cards and tapping but no "mana" pool etc. Star Wars choose to find another way to deal with tapping by just using activation of "mana" to power everything and have no tapping.
As for Dungeons and Dragons, it could have been patented when it released, but now it is to far gone and was never done. There is no way to go back. Also, the OGL for 3.0 and 3.5 basic ensures that all dice driven RPGs are never going to be patented unless someone finds a really radically way to add 3 innovations to the RPG model. Attempts have been done, but the purity of RPGs doesn't allow it to become accessory laden or modified through non-mathematical complications very easily. To my understanding (and I believe Ryan Dancy said this in the open letter about the TSR acqusition) that role playing games are impossible to patent at this point in the industry.
On another point, basic game systems cannot be patented. Rolling dice, doing math, reading, drawing, acting, hands of cards, decks of cards, moving pieces on a board or graph, etc are all considered things that are the medium of game playing. These things cannot be owned no matter how original you think you're being with them.
This is how so many of those Pictionary/ Trivia/ Cranium type games exist. Also, if you look at the patents on that link above, they are games with added game features, often electronic ones (dark tower for example).
The best way to OWN a game is with good gameplay, great artwork, quality pieces and a solid Brand and Trademark that people rememeber and are drawn to. The overall package can be owned, and it is there that you market your product and get people to play your game. Again, Cranium is a good example of a company doing this successfully then using their niche market in Starbucks and gaming stores to grow out into the mass market with off shoots and kid variant games. Nothing in the game is patent worthy, nearly all of it is copyrighted (artwork) and trademarks (character names, cranium clay, etc).
