I think what bpp might be saying is that he doesn't see a way (on his Japanese taxes) to deduct the Japanese tax component already paid out on his behalf by a US mutual fund holding Japanese investments.
You're right that in the US we have the Foreign Tax Credit but maybe he can't find a Japanese analog.
nun, excellent point on SS. Being retired and thus not working here there's no issue for me personally to have to try and broker payments from two countries, but that could be the case for others. I believe when/if my paltry SS come in I can get it direct-deposited to an Italian bank.
bpp, tough question! I really don't know if I will want to "retire" here*
(that is, grow old here). I'll let you know in 10 or 20 years... Health care coming back would be a big cost issue, but on other levels life in the US is easier for oldsters (and everyone else). I still feel somewhat 'on vacation'. My Italian DH has started to fit in better in our new town; he knows the ropes. I miss a sense of 'agency' and give up on things that I might be doing if I were in the US, as here they are "too difficult". Keeps $ in my pocket, though, that way.. Will depend, as well, on what our family situations are further down the road. Just living the Jello life, I guess!*