The graphic with that article and the article itself is incorrect. The NBN will be capable of offering speeds (eventually) of 1000 Mbs, which is equal to that of South Korea. Initally the maximum plan is 100Mbs, however using the fibre optic cable it is possible to offer speeds of 1000Mbs althoguh to achieve those speeds you have to upgrade the hubs and ports at the exchanges (which will occur over the next few years gradually). So the speed is/will actually be the same as South Korea.
As for the cost, I don't know how many times larger Australia is that South Korea, although at a guess it is more than 24 times larger in land mass so its no surprise it will cost more.