Alright, the "d"- word
Fine bones occur in Arabians, no doubt. Mainly bloodlines who are being bred for halter shows only. Much like halter QH, over muscled on fine bones and tiny feet. Not, contrary to what some believe, in certain types of Arabians, I.e Egyptians or the Bey Shah's. It runs in breeding farms, where nobody is interested in good bone and only pretty head and neck counts. My SE gelding had 8 1/2" cannon bone and was a solid 15.2hh with a built like a stock horse.
See what I mean? Can't generalize. Another thing to consider, Arabians have greater bone density than other breeds, so circumference is not all that matters.