Diablo caters to the idiot masses of the mainstream audience. So did Britney Spears. You may consider her a singer, but I consider her crap. You may consider Diablo a RPG, while I consider it crap. I rather play Might and Magic 9 than play a session of Diablo 1 and 2.
Fable is more a action/adventure game than a CRPG.
Yes, Diablo has stats, equipment, levels, blah blah blah. All the things that are found in CRPGs but there is something that Diablo lacks which a CRPG has. That is dialog that allows one to role play their character. I don't see any good dialog options in Diablo like there is in Fallout, KotOR, Planescape Torment, and the such. Character interaction, in more ways than just swing a sword, is needed to make a CRPG into a CRPG.