(I would like to point out I sort of agree with you on this one, companies are a bit too quick to "globalize" themselves when it suits, but it's fun to play devils advocate)
How is this any different than a person who works over here for say a US based company who then travels to the US for work purposes but they are been paid less than their US counterparts? Should the Australian be paid at a higher rate whilst they are in the US simply because their counterparts are entitled to a higher wage? Should they not be paid simply an allowance which allows them to live whilst there, and yet still paid at a rate which is appropriate for their job over here?
On this forum, there is a lot of people who travel for work, when they travel they are still paid based on Australian wages, not the wages of where they are visiting. I'd imagine the OS cabin crew working the SYD-MEL would have some sort of travel allowance to cover the costs of traveling here in AU, but again their wages would remain what they would be earning had they not traveled here.
the US counterpart might have something to say about it however!
its an interesting issue. personally, if I was assigned to working overseas for 'x' amount of time I would be weighing up the various factors... is my accommodation included? what work experience am I getting? how much fun will I be having in that other country (sightseeing, socializing, having a break from the routine of home)? is this part of a development plan so I can return to a higher position in Australia?
would I be happy to accept a one or two year posting where I know I am being used only because I represent a cheaper labour cost to the company? probably not (but again that depends on my ability to move and commitments such as a mortgage back home).
but with cabin crew we are talking about (essentially) a service type industry, with pressures that potentially lead to exploitation (if you don't want the job there are 10,000 queuing up to take it). one of the things Australia can be proud of (at least somewhere way back in the past) is its union movement... 8 hours work, 8 hours rest, 8 hours play. we have advancements in equal pay, maternity leave, careers leave, and protection from unfair dismissal to name a few things.
i don't necessarily have a problem with an Australian company off shore employing off shore workers at local rates (provided there is no exploitation and working conditions are safe). but I have a problem with importing labour for the sole purpose of lowering costs and circumventing Australian expectations. it is essentially exploiting that person.
would we say it is acceptable if an Australian company turned to its married female employees and told them they only needed half pay because their husbands already earn a living and that should be enough? of course not. so why should we get away with the argument that a Thai employee only 'needs' x amount of dollars and so that's all their worth? in Australia one of the measures we use for wages is productivity... and so by that argument, if a person is doing the same work, why not pay them the same?
if you are employed by Thai airways... you can pay accordingly. but if you are employed by an Australian, flying into Australia, taking the job of an Australian, then you should be paid the same as an Australian.