most people bought the iPhone 4 on a 24 month contract, those people probably wont by the iPhone 4S due to the high cost of early termination fees for little gain. (of course some people will which is just a bonus).
This cycle is pretty clever as it pretty much guarentees majority of iPhone 4 holders will upgrade to iPhone 5, whilst simaltanously giving a decent bump in sales to people who have had there friends talking up the iPhone 4 for a year a chance to one-up them.
I'm one of them and I don't see a compelling enough reason to upgrade at this point (iPhone or Android). Siri looks interesting, but it's not a feature worth locking myself into another 24 month contract for.
All the Australian networks are moving to 4G, so IMO it's a good time to wait for the next gen of LTE handsets. As with the original iPhone, I suspect it was just too early for Apple to switch.