I made an analysis of Japanese developers this generation. You can see the thread here: http://www.vgchartz.com/forum/thread.php?id=45223&start=0
There is one interesting fact and it's that 3rd party Japanese developed games have almost the same marketshares on the different consoles as those of the consoles. There is a slight advantage towards the PS3. So, if they have the problem, it's not necessarily because they have not supported the Wii.
How many cups of darkness have I drank over the years? Even I don't know...