Probably because Facebook decided to "invade" and set up office, whereas Twitter worked with Tokyo-based Digital Garage to localise Twitter for the Japanese mar

Probably because Facebook decided to "invade" and set up office, whereas Twitter worked with Tokyo-based Digital Garage to localise Twitter for the Japanese market (and attempt to provide extended services geared for the Japanese market). Twitter also doesn't require your real name - all they care about is that impersonators specify that they are parody and not genuine.