A question just out of curiosity...

I was looking at J flights AKL-LHR and noticed that JAL have a very good deal flying via NRT. When JAL join OW next year it seems like the best route to go to clock the miles : AKL-NRT is a 777 codeshare with NZ, and NRT-LHR is also 777, full lie-flat seats as opposed to QF, TG, Emirates.

Anyway, the quick question is why are taxes so high flying via NRT? They're nearly double other airlines on the regular routings (SIN, BKK, etc). Is this the high cost of NRT or is it peculiar to flying JAL?