Very very clever marketing.
Apart from the millions of dollars of free advertising and publicity, guess what?
Thats 15,000 seats of unused Virgin capacity (Wirraways bit over 7.5%) that Ansett wont get a sniff at over the period they are starting up.
I would take a bet that people being what they are, they will retain a goodly part of the return passage.
Make no mistake this business wins or loses on mere %age points of overall traffic gained or lost.
In any event any new entrant like AN in this environment is going to have a long hard row to hoe.