Due to the higher friction of trading items in Diablo 2 as compared to that of D3 (auction house) there's an assumption that the drop rate of quality items in Diablo 2 was higher than in D3. Further, in D3 the items are a lot more liquid due to the ease of exchanging on the auction house and so there's a feeling of instead focusing solely on collecting gold and then choosing an item on the auction house rather than enjoying "slot machine" mechanics.

http://www.alexc.me/a-scientific-explanation-why-diablo-3-is...