Background: Our qualification for a "main" genre is any genre that "stands alone" -- meaning, a genre that is clearly not a subgenre of anything else. For example, "baseball" is not a main genre because it clearly falls under the Sports genre. Same goes for shooter (sub of Action), card games (sub of strategy), etc. Pretty straightforward. So, following that logic, RPG was a sub of Adventure, because most RPGs are adventures -- they have a storyline, have path branches, etc.
This taxonomy was met with some resistance, but most arguments were easily dismissed -- until last month, when a fellow software-collecting friend of mine came up with definitive proof that RPG could indeed "stand alone": Rogue. Rogue-like games, like Hack/NetHack, Moria, Rogue itself, etc. are RPGs with little or no story. There may be a story, but it is less than 1% of the game's gameplay value and cannot be considered as the main focus of the game. (This is why Half-Life is not considered an Adventure, because although it has a very engaging story, that story is 100% linear and unalterable and not the main focus of gameplay.)
To further prove that RPG needs to move to the main genre list, let's compare my favorite Rogue-like game, Hack, to all of the main genres to see if it's a fit:
Action: No. (Hack is turn-based, so it does not meet the requirements for action.)
Adventure: No. (There is a premise, but no real story paths/branches -- there isn't even any story to be discovered.)
Racing / Driving: No.
Strategy: No. (There is a tiny amount of strategy involved, but it is not the main focus of gameplay.)
So if it does not fit, then its genre must be considered a Main one. And that's exactly what I've done as of about 10 minutes ago. The home page and some underlying pages will need some time to catch up due to caching, but if you create a new game entry you will see that Role-Playing has joined the Main (basic) genre list.
One ironic thing about this change is that most of the RPG games we have in the database do not need their genres edited to take out "Adventure", because over 90% of RPGs are indeed Adventure games (they have a significant plot/story, including the ability in some for the story to be altered or branched). However, if you run across any RPGs in our database that you feel should have Adventure removed, submit a Correction using the link at the bottom of the page and we'll take care of it.