Airbus has had experience in building tanker aircraft.
http://en.wikipedia.org/wiki/Airbus_A310_MRTT
Australia had similar demands to the USAF in seeking a tanker replacement. It selected the A330 MRTT.
It can carry more fuel further, with a larger cargo space as well. Yes it is more expensive but it suits Australia's needs better as there are less airports to land at in Australia (have a look on a map and you will see a lot of nothing!) and a long distance to anywhere outside Australia