So, what, D&D owns fantasy or something? Ha ha.... no. I don't recall Diablo ever messing about with THAC0 or D&D specific rules. Cribbing "level up" mechanics

So, what, D&D owns fantasy or something? Ha ha.... no. I don't recall Diablo ever messing about with THAC0 or D&D specific rules. Cribbing "level up" mechanics is about the same level as music sampling the amen break. An enormous debt might be owed, sure, but the concept is a public good now and said debt is uncollectable.