Has there ever really been a time when D&D was not at (or near) the top of the RPG pile? It has been the gateway to nearly everyone who has ever dabbled, ventured, or committed themselves to the one true king-daddy of all roleplaying games. Aside from some keen insights and interesting factoids, this article (and many others like it) are no-brainers.
But let's continue to be awed and amazed at the nearly 50-year run at the top of the industry. I mean, I'm still playing the game; just not the current edition.