Third Party Devs have made up their minds about the Wii.

[Soma]

Nintendo DO need third parties, they can just make a certain amount of games a year and need all diversity as possible. In fact, part of Wii success is thanks to third party games.

With that said, if Big third party companies do not want to invest on it (with good games and good advertisement), then it's a huge opportunity for small studios to capitalize. Suda 51 may have a huge opportunity with No More Heroes 2, High Voltage with the Grinder and so on.