Big Mach,
Sorry, but your thinking is wrong. Just because CX is a HK based company doesn't give it the right to base crew wherever they like and disregard local labour laws or tax law. Your idea shipping companies base crew how they please and ignore the host country is rubbish. You'll find they fly the crew to whatever country they are picking the ship up from, they don't reside in-country as CX crew did/do.
There are no international conventions as you claim if the crew are to reside in that country. In the past all that happened was the host countries ignored the situation (aviation) as overall it was minor, which it now no longer is. There are Australian crews commuting to Japan for three airlines and a bloody whole host of companies in China. The ATO is very keen on this.