I would have to agree with most other posters that this assessment is a bit harsh. I fly Jetstar domestic occasionally and I find them acceptable. Cabin crew have always been pleasant. Really a case of getting what you pay for. I would suggest a large reason for the poor result comes from a sense of entitlement that a lot of Australians (and others) suffer from. Pay $50 for a return ticket and then expect an experience commensurate with someone who paid $1000 for the same trip and is sitting up the front on Qantas, sipping a glass of bubbly. When reality fails to match expectation and along comes a survey, blame the airline. I've heard people bagging the cabin crew but I always wonder. Politeness begets politeness and cabin crew on Jetstar would be a tough job.
My biggest gripe with Jetstar is their punctuality. If I book with them, I can have no expectation of getting off the plane at the time I need to, therefore, I generally avoid them.