Actually it has more to do with different search engines than it is with taxes.

CathayPacific.com's CRS is based in HKG and is wired through their own CRS, whereas the CX-USA's search engine is wired through an affiliate agency that uses SABRE.

It's not to say who is right and who isn't. CX's fare however, might be that that certain ticket does not earn miles hence the zero count. CX-USA's website doesn't as it has to take into consideration of what class it is booked into in the first place.