I would imagine that the raw products (meat etc...) account for a very
small portion of the burger price. It is manpower and general expenses
(rent) that likely make the most of the burger price. In that field,
and despite the high cost of space in Japan, I guess a high sales
turnover at each outlet enables to substantially lower the cost of each
burger served. That is what would make the difference with Australia,
in my opinion. In short, the density of the population makes the
"distribution" of burgers more efficient.