Back in the good old days (when I used to walk to and from school in a blizzard uphill in both directions), my Los Angeles County OW certification took you through most of what is in today's OW, AOW and Rescue. It was a three week course though and the cost today would probably be a barrier for many new divers (hmmm). Since a number of younger instructors (mostly from PADI) weren't aware of the LAC certification requirements, they often made me do check out dives. I found a PADI instructor in Australia who recognized my card and gave me a PADI AOW for the cost of the book. I also did a PADI Rescue cert with another great PADI instructor. Personally, I consider all three certs necessary to develop a decently trained diver.