Freehills,
This tax sounds like a sales tax which should be (and probably is) collected at the time of sale; just like other airport taxes, fees, and surcharges. Why it would ever be reported as revenue and then taxed after the fact, I don't know. Maybe it makes no difference either way.
WRT to the KLM flight, I suspect this has more to do with softened demand to and from Europe due to the economy there. This can only be considered good news for CX as we will undoubtedly pick up some of those passengers and cargo.