FMC equipped aircraft have a function known as "cost index". It is a function of fuel costs vs other hour variable costs and allows the FMC to calculate the most economical speeds for climb, cruise and descent. As fuel cost's rise, so the economy of operation is biased more towards fuel conservation (and thus slower speeds).
I dare say Qantas has re-calculated its' cost indicies and this has resulted in slower speeds.
I know in my operation we are operating with a signifigantly lower cost index (i.e. higher fuel costs) than a year ago, and this has resulted in climb and descent speeds around 10-15kts slower, and operating Mach numbers .01-.03 less.
Gotta love those A-Rabs!!