It's more not getting on the ship in the first place than jumping off, but I digress. Right now, a lot of Japanese developers are falling into two groups. You've got the ones making the decidedly "Japanese" games and sticking to handhelds, and you've got the ones reaching out to western audiences and making games for the HD consoles, sometimes in-house, a lot of times outsourced.
Now, you've got exceptions like Sega, but I think this setup works for most developers, and if the Wii continues to flounder like it has been, I'm not sure they'll see any reason to rock the boat.
Like I said, I know the Wii has some big guns coming, like DQX and MH3, but it needs better, more consistent support around those, and right now, publishers are getting plenty of water at the wells they're already drinking from.