As others have pointed out, I think the main difference is that Virgin and others just starting up do not have these facilities yet, where Qantas who have been around forever already have everything they could possibly need IN Australia.
I am surprised Qantas would be allowed to send any heavy maintenance off shore, back in the 1960s Ansett planned to send their Carvairs to Hong Kong for due heavy maintenance and it was blocked by the then Australian Government as it was against the National Interest.
The then Government wanted to keep the work here in Australia, partly to keep all the already established Ansett facilities open and employing Aussies, but also they said to keep the facilities here in case of any International unrest or wars, and this was before all of the terrorism etc, so you would think I would apply even more today to Qantas being basically the only facilities left here.