If the Japanese only like casual games, then why is Final Fantasy thought to be the most popular game in Japan, Crisis Core Final Fantasy VII sold really well, but it does not appear to be a very casual game.
If they only like casual games, then how will Final Fantasy XIII be the saviour of the PS3.

It's just a slow period for Japan

Yea how are FF, DQ, and Fatal Frame casual games? And what is this about them not playing long games anymore? Did you see the sales for DQ IV this week? I think that the Japanese have a certain "ultra-hardcore" element to them that they will play old remakes like this. When a game comes out that they really want, it will sell very well. I expect MGS4 and DQ 9 to do really well there.

Another thing is that they are very conservative with money. Japan has one of the highest savings rates in the world. The US is geared towards consumption, so this could have something to do with it. Just my 2 cents.

Japan is a much bigger market than UK, don't compare a market that is in holiday sales with one that is still in the slowest period of the year. If you include handhelds Japan sells way more than UK does, if you are just talking about consoles Japan sell about 50% more consoles, still a significant amount.

DS has sold more in Japan than in North America and all of others, that is an amazing stat.

sales dont go up untill december

Japan Holiday for gift giving (The way I understand the holiday it is more a holiday where adults give kids cash) is early in January. With that in mind the bump in sales doesnt happen until well into December and hits its peak the first week of January.

 Market percentage, not population.  Market percentage wise Japan is about anywhere from 16-20% of the market.  UK is about 10-15% thereabout.  Most likely it's the middle of the 2 or about 13% and 18% respectively.  Its mainly software sales that keeps Japan above UK. 

Japan has around a pop of 100 million
UK had about 40 million

I'd say the UK is more hardcore right now...