I agree with Charliecho. Due to the creative/sandbox mode and the fact you can do so much with it means that just about anything is possible. However I do not think that user created maps would count as making 'Minecraft' an RPG (or any other genre for that matter). The game itself "Minecraft" is not 'made' any genre due to custom maps being made for it.
There are three main aspects to game Minecraft.
Creative is just that; you can play about with everything to see how it all the things work and there is so much to do that it would be difficult for many to get bored. Plus you can create your own worlds/games for other people to play in. Creative mode is not RPG though.
Secondly you can play the adventure mode and while this contains RPG elements (as do many other games that are not classed as RPG) it can not be classed as an RPG. I would say that adventure mode is again, just that; adventure. Just like, say, Zelda is not really an RPG but instead an action/adventure game with a large amount of RPG elements. I guess what I am saying is, are you confused to what an RPG actually is and not mixing it up with an action/adventure game?
Thirdly, you can play users custom maps which in themselves can be many different genres (but see first note) but I think Minecraft is too limited/tedious to be able to make a true RPG custom map. I guess it is possible but would be a crazy task to achieve in terms of mechanics required and time needed. I know it is sandbox but you still only have a limited amount of things to tinker with.
I certainly agree that things added to the game over time have also added RPG elements to the game but not to the point where it could be considered as an actual RPG.
That is what I think anyway.
