I'm not sure; I am sure that I never implemented AO to its fullest because it is so hard to do so IMO.
The biggest difference is that all kids are doing the same general time frame and that there are fewer books, done better. There are extra helpings for kids who read fast or need more but I no longer feel like all we do is read and narrate all day with no end in sight and no help in figuring out which of the "free reads" are useful or important. (Some of the AO people have their kids read all the free reads; I can't imagine and I have one really fast reader.) There is more coordination between the "free reads" and your work.
Nicole Williams also has implemented Natural History in a much more holistic way now that the PNEU works are available to read online and she was able to do more reading on what the schools actually did.
I guess the biggest difference seems to be that all the kids are on the same history schedule? and they provided you with daily schedules with time limits? Otherwise there are the same amount of subjects in both programs.