It's incredible how much high quality restaurant food, groceries and snacks like these that Japan has had for a relatively low price as compared to other wealthy nations. It was quite noticeable for me the last 2 times I went to Tokyo/Kyoto/Osaka, as a visitor from the US, that food costs were pretty much never an issue. I guess the dollar being strong has something to do with that.
One big difference I see between the two is the level of service expected. In the US, the waiters are constantly interrupting and bugging the customers, hoping for a bigger tip. In Europe and Japan, this doesn't happen; you need to signal to your server that you need something, and there generally seems to be less staff as a result, which reduces costs.
Basically, this is just another way that America is broken compared to the rest of the developed world, and it's not just the strength of the dollar.