Hmm... I don't know. I have the Original Diablo and Diablo II with add-on separate and they _ARE NOT_ the package deal that you may find in some stores.
I am not sure I even want to try to play them any more.. Besides they do not meet today's computer requirements. 1998-2000's maybe, but not now.
As for Diablo III? What is it this time? Heaven and Earth fighting against Hell?
If they really would like me to play their series again I would suggest that they find and not only buy the rights to Diablo 1's add-on "Hellfire", but also add it to the complete Diablo package.
"Hellfire"? It was made by Sierra who was bought out by Activision. Activision does not have "Hellfire" in its archives. I know because I looked.