It is quite perplexing.  I really don't think it's because of small apartments.  It's mainly because nobody here has ever heard of it.  The JPY market on MtGox has extremely low volume, despite the fact that it's very fast and easy to get yen onto MtGox.

The other weird thing is that foreign exchange trading works as a de facto legal gambling industry here.  I don't have any good figures for the popularity, but in subways / trains / TV there are countless ads for FX trading platforms.  Mostly JPY / USD / EUR I guess.  Not sure if you actually get to take delivery or if it's more of a derivative like the CFD stuff which seems more popular in the EU.

But yeah.  No bitcoin awareness in Japan, no media, nothing.  Who knows why.  Might be that people are pretty old & conservative; I wouldn't expect my grandparents, nor Warren Buffet, nor most Japanese elderly people to understand bitcoin.