The open gaming license essentially says "you can use our game to make up anything you want", in a way, it's 'legal plagiarism'. As one lawyer said at the time (I'm paraphrasing) ..."The game is dice and statistical math, how would you regulate that ?" Believe me , they tried to regulate it. All through the 80's and 90's , there were tricky lawsuits related to copyright infringement, and the OPEN GAMING LICENSE was WotC's answer to put a stop to it. Why couldn't they just make it illegal to use the rules? Well, these rules everybody is stealing and changing to make their own game are partially derived from an article written long enough ago to be considered "public domain" ( ie "open soucre" material). This legal snag tends to turn off copyright and intellectual property lawyers. It's an article written by HG Wellls ( and since it wasn't in print for 75 years, it became "public domain"), and legally, is "free". TSR managed to protect the rights to the games, but not the rules, per say, since it's a 'reinterpretation' of this HG Well's article. This is what they call "a gray area".
Back in the 1880's HG Wells (of War of the Worlds fame) invented the "war game". Yes, when he wasn't turning out classic sci-fi novels, he was inventing a new kind of game. He drew up the instructions in an article: basically, a game played with miniature figurines (of soldiers, calvary units etc) and models of castles and towers. Each piece was assigned points and a number of spaces it could move. Craftsmanship of the miniatures is a big fetish here. These are elaborate set ups, with working (doll house like) cut aways, opening / closing drawbridges and so forth. Then you move your men around, and plan (in miniature) large scale 'war games'. It's was a nice diversion to help take your mind off of Jack the Ripper.
Now a days, if you are a hot shot video game maker, and you are hired to make the next Spider Man video ("movie tie-in") game , you already know you'll need to add certain devices to play the game. For instance, the player, as Spider Man, will need a virtual life bar, a power bar, a map or layout of the city, and inventory list of items you need to work through the game. If your running the new Sims game, you need similar stuff. Ditto for those computer games...everything from Civilization to the new Tom Clancy "first person shooter" games. All that stuff, you have to thank, in a round about way, HG Wells. Because it's public domain, anyone can use these "devices". His rules on minature war gaming have been worked into countless games. But we're getting ahead of ourselves here.
"So, HG Wells plays with toys...So what?" So, flash forward to the 1950's...Boardgames are huge moneymakers...Sure they've been around for years, but when the mass production apparatus is put into place, they go global. And in a few years, RISK and STRATEGO become hot hot hot! And they are , basically, HG Well's miniature soldier game...for kids! But the game that didn't make it as big were these other games, which added the "alternate history" dynamic to the game. Imagine how the south could have won the Civil War...what would Germany need to do, in order to win WWII...Yeah, well, these games appealed to history buffs...and Gary Gygax and Dave Arnoson were big history buffs. Up Next! NERDS UNITE!