Yeah, I think PS3 has seen its best days already in Japan (so has Wii, but the decline will be slower). I don't really see a lot of system mover for PS3 besides FFIV and GT5. Two of the biggest franchises in Japan, Monster Hunter, and Dragon Quest, are now on Wii. Wii Party, Last Story, Xenoblade, Zelda, and Wii Relax should also be big system movers.
Despite a drought of games now, Nintendo seems to have that abilty to create system sellers that are evergreen titles almost at will. Sony has the edge in 3rd party support obviously, but the popularity of many once big franchises in Japan are dwindling. This means they have to rely more on new ips, which don't fare too well in Japan, at least core ones. So I think ultimatlely, Nintendo still has the edge in Japan.