As other ppruners have mentioned, a fuel related incident really is the last thing the rat needs at the moment. If a hull loss were to be the result of A fuel exhaustion incident there would be no airline left to speak of.
Hull loss due to insufficient fuel? I can think of a number of things that could possibly lead to a hull loss in airlines generally and QF specifically. Running the tanks dry and the aircraft subsequently augering in is a very, very, long way down that list!
Carry a ton of fuel between Sydney and Perth on a 767 and you'll burn 250kgs. Carry 4 ton and you'll burn 1 of it meaning you'll only have an additional 3 ton over the top of Perth. THAT is a significant amount of money. If you do that across all the services that QF (and Virgin and J*) fly daily in Australia and you're talking about millions of dollars a week. It's not just as simple as carrying the extra fuel all the time.