I don't think that anybody ever knows who the Jap Prime Minister is...I bet if you gave a pop quiz to the US Senators and congresscritters only a small percent would know, and even on the foreign relations committees there's be a fair number, maybe more than half who wouldn't know. It seems to be one of those facts that is unimportant to know. I wonder how many Japanese know...
When someone at a COSCO checkout line back in the US (upon hearing someone is a visiting 'expat' just in from Tokyo, actually asks if 'do they have TV over there in Japan?', or 'how long by traing from Tokyo to Hong Kong', somebody indeed needs geography and culture lessons about one of the most important nations on the face of the earth--let alone come out of a brain dead knowledge base about who Japanese prime ministers are.
Just wait till Shintaro Ishihara becomes PM some day. THEN most Americans will know who is the big chief at Nagatacho.
I can never forget the one named "Takeshita."