firepussy you have unwittingly hit the nail on the head with your comment about "protected species".
As a major airline Group you would really hope that Qantas could start and nurture an LCC better and cheaper than could a stand-alone competitor. In fact it would be absolutely appalling if it couldn't do so. So Qantas is "protecting" JQ by effectively allowing it to operate at the QF Group's marginal cost. (big simplified generality but you get the drift).
In the same way JQ is "protecting" Qantas. If you have the time and wits, get a calculator and see what happens to the QF books if you take a JQ sized chunk of revenue and costs out of the Groups results. Not pretty at all. Then go the one step further that, firepussy, marks the professional vs the amateur analyst, and imagine that a stand-alone LCC was stealing QF traffic and that as a result QF yields and Load Factor fell by say 3%. Throw in high fuel prices and a sagging world economy if you're good at scenario analysis.
That would be, for the Qantas Group the China Syndrome, a real meltdown. Yes....happened to United, Delta, Northwest, American. Pension plans headed south, planes parked, wages ruthlessly cut, routes folded etc etc. Not even vaguely pretty.
The essence of symbiosis, synergy, collective strength, economies of scope or whatever you call it is that the QF Group's two brand strategy secures all Group jobs to the benefit of all. It is not perfect.....it has been poorly handled....it is executed by some folks with way too much wide-eyed naivety and ideology.....but it works and for that all QF Group employees should be thankful.
And back to the scenario analysis....add to your thoughts a near future sceanrio with Tiger flying 30 aircraft domestically feeding into a Singapore Airlines operation on Pacific routes with the A380 and the 777-300ER. Virgin dying or contracting and desperately running "two for one" deals that slash yields.....at that time a QF Board that didn't have already have in place a mature Jetstar strategy would be criminally derelict.