Yea, that is good point. I used to see signs at duty free shops in the U.S. airports with flights to Narita warning transferring passenger regarding purchasing liquid items. I am sure employees at duty free shops make sure that passengers are terminating at Narita, not connecting to other flights at Narita. But again, if clearing customs at Narita and transferring to domestic flights, then domestic flights in Japan allow more than 100 mL bottle of liquid. Actually when I transferred to domestic flight Narita-Haneda, check in agent at Haneda (ANA) encouraged me to carry my duty free liquor as carry on rather than put into my check baggage.