IIRC Qantas had a minimum number of pax required to be in the exits (I believe it was 1 per row on the 737, so 4 pax) when the total pax count was under a certain amount... cannot remember for sure now though, sorry. Perhaps a current Q hostie can tell you. I do know the requirement didn't exist on the 767 b/c crew are seated in between those overwing exits.