Aus_Mal - I frankly am amazed they'd quote a RTW that includes taxes, but can't see I am reading that wrong?
Offer seems really short of hard detail, or a weblink to check data on, and all they say on the tax front is - "Price quoted is based on an itinerary Sydney, Los Angeles, London, Bangkok and Sydney."
Even so, that is probably $400-$500 in taxes right there I'd guess? With the $200 credit, it effectively becomes a ~$A1300 + tax RTW.
Sensational deal I would have thought - depending on what fare classes they book them in.