"Average" is a bit of a red herring when it's being used by Australia Post...

They said the same thing when they overhauled the international parcel prices earlier in the year, and it was technically true because they decreased the pricing of some international express services, but the actual increase to all other parcel services was 10%-15%.

I don't expect we'll see any decreases for domestic prices, though, more like less popular services may only increase 1%, while more popular ones will increase 5% or something.