Some insightful replies, I agree size, price and games appealing to the Japanese market are the main driving factors.
All will be addressed in due time though, Sony stated that they are going to release a cheaper slimline PS3 at some point and it has the most yet unreleased anticipated games line-up.
The PS2 had the most important Japanese RPG games Final Fantasy and Dragon Quest available within the first year of global PS2 release. It's just a matter of time for the PS3 to really breakthrough in Japan.







