right, but that's the US. In the US there are plenty of other people who don't speak english for the non-english speakers to chill with. In the US we have ethnic neighborhoods which cater specifically to people of certain ethnicities who may not be able to read english.
Japan is an island. Only 1,310,545 people there are foreigners, as opposed to the US where 31,107,890 people are foreign born. It also doesn't help the situation that the Japanese are generally(sweeping generalization here) xenophobic. Yes, you can survive in Japan not knowing Japanese, but it'll be tough as most of their signs, books, television shows, and most of the people you'll meet will only speak Japanese. From what I understand from people I talk to who have been there, it's a very nice place to visit but living there would get very very lonely.