I do have the impression Tokyo is getting similar dynamics to the rest of the world on this front: builders don't care where the money is coming from and so if money from outside the country can get buildings built they're happy.
A friend of mine moved into a sold-out Yokohama tower mansion recently... and despite the bike and car parking being fully booked even more than 6 months in it was _quite_ empty. I have a feeling a lot of people are buying into the market expecting to get easy rental money and not really seeing it.