There's also the ubiquity of smartphones to consider. I was there this month and everyone was using their iphone to trap in and out.

And I do mean iPhone, not generic smartphone. It seems that in Japan, iPhone is absolutely dominant and may (??) have some sort of additional chip in it (Felica?) that allows it to be used for other shopping. Presumably that is not essential for transit use as my friend with a US iphone was able to tap and pay using Apple Pay.

Perhaps a Japan reader can comment. Android doesnt seem to be supported much, and certainly not for overseas phones, as this link describes.

https://support.google.com/wallet/answer/13314575?hl=en

Quite a bummer for tourists, I'd have thought.