I notice a lot of people mention Diablo and Zelda, and to me these are not real RPG games.
To me a roleplaying game is where you roleplay as your own character(Giving you multiple choices and different ways to reach your goals).
When you play Diablo, are you roleplaying a mighty warrior or mage? Well no.. unless your roleplaying as a person with a single intent to go around and kill things for treasure, experience and gear.
Now for Zelda... Do you have choice to rescue the princess or let her get eaten by the Grue? (you Zork players know what a Grue is!) In every Zelda game I've played (and not many.. I might add...), you've always only had one choice, one path to take.
If you are playing a game where 'action' or 'combat' is the only role you assume, why not call it an action game?
Keep RPG genre for games that you can make storyline choices, eat apples, and pickpocket the local merchants!