Flawed logic.
A causasian actor can play English, American, Australian, Russian, Scandanavian etc as their features are largely similiar. Chinese and Japanese people have different features and do not look the same. They are easily distinguishable. Same goes for Thai, Tibetan, Mongolian.............
Seriously, the logic that says orientals kinda look the same, meaning that a Chinese person can therefore play a Japanese person, is like saying an actor who has a tan can play a character who is half-caste.
Tell you what - try going up to a Chinese person and asking whereabouts in Japan they're from (or vice-versa) and see their reaction.
That should be fun.