if languages were RPGs

C=Diablo
C++=Diablo2
C#=WOW
Java=Final Fantasy 11
Assembler=Adventure MUD
BASIC=Ultima Online
Haskell=OpenCobalt
Lisp=Second Life
Forth=Myst

RPG isn't a statistical/gambling game.
believe it or not, R stands for Role not Random.
Diablo is "RPG" only becuase of backstory and quests.
Now if you remove all quests and NPCs from Diablo, the game won't change much. But it will not be a RPG anymore, becoming a hack and slash simulator. To be abstracted further, Diablo at its core has the monster-item hunt elements, which could be represented by a single room spawning a random monster(which drops a random item) or item, with objective to get the best item set(to maximize statistics of a given character). The rest is just "RPG elements" which bear no significance to the game.