From my perspective it's only the smaller Japanese companies that are really lining up behind the Wii in Japan. It's pretty obvious why they're doing it since they rely so heavily on Japan for sales of their games. A large majority of those games will either never come to the West or if they do they will have little impact.
The bigger developers on the other hand realize that the Wii isn't the PS2 (for third parties) and are looking to build their presence outside of Japan in order to make up for the Wii's domination of Japan. It's pretty obvious what is happening when you listen to someone from Square Enix, Konami, etc, talk about focusing their games on the West.
What some people here seem to be hoping for (that the Wii will become for third party major exclusives what the PS2 was), I just don't see happening and I think those that do think it's going to happen are only fooling themselves.