Those factors influence prices to consumers only if and when the seller refuses to lower its markups. With a 61% markup, I think Apple has some wiggle room.
You didn't actually read Apple's response, did you? 61% on downloadable media (what idiot started calling it "digital"? ) happens because Apple pays 61% more to the record companies.
For computers, it seems you don't understand the situation.
Go back ten years ago. 1 US$ = 2 Aus$. Say a computer was sold in the USA for $1000. US$900 for building the computer, US$100 for stores, employees etc. In Australia, they charged Aus$2000. Aus$1800 for the computer, Aus$200 for stores, employees etc.
Now, 1 US$ = 1 Aus$. The cost of building the computer is now Aus$900. The rest of the cost is unchanged Aus$200. So the same computer is sold for Aus$1100. So really the Australians should be happy that their computer is now a lot cheaper than ten years ago.
However, Aus$1100 = US$1100, which is more than in the USA. They complain. But the reason for the price difference is that the cost of selling the computer is Aus$200 = US$200, whereas in the USA the cost is US$100. The Australians make (right now) more money than people in the USA, but you think that Apple should eat that cost. Why?
So you really think Apple should make less profit in Australia because Australians make more money?
----------
The publishers sued somebody who bought textbooks overseas for cheap and sold them to American students for less than list price. He got sued by the publishers, and dragged all the way to the Supreme Court.
(BTW, the USSC decided that he was within his rights due to the First Sale Doctrine.)
so there are two points here: until earlier this week, it was not clear that it was ok to do what you suggest with physical media, and if you try it with something other than college textbooks, you may well get sued by the publisher.
However, that was about resale. You were (in the USA) always allowed to buy books abroad. The question was whether the First Sale doctrine that allows you to resell books that you bought applied to books bought in foreign countries. The law says it applies to all books that were "lawfully produced under this act". Book publishers said "under this act" means "in the country where that act is law, that is the USA". The defense claimed, and turned out to be right, saying that "under this act" means "produced in a way that follows the rules of the US law". So now you can resell in the USA any book that was produced according to US copyright law, anywhere in the world.