The AOC split I'm guessing has more to do with the fact that foreigners can own 100% of a domestic airline in Australia ala Tiger, Rex, Skywest, Cobham etc. They can't own majority international airlines.
The split was organised probably in anticipation of the QSA being relaxed one day, the domestic operation to being able to be essentially owned by foreigners and being then able to have defacto control over the international operation, exactly what Qantas accuse Virgin of doing.
However, that's all just a guess.