Lets take a look
Jetstar A320 are covered by warrenty for 2 years, Maint costs are recovered if "defect confirmed" by Airbus or component manufacturer.
Jetstar A330 are leased from QF, I do not know who pays for the maintenance, but, if I had a lease car, and it broke down , the repair would be paid by the leasing company.
Again for the A320 after warrenty..be interesting to see if Jetstars, or Qantas's maintenance costs, (and therefore profit), increase or decline as the A320's get older.
To a dumb ass like me, maths can make anything look good, you just have to know how to play