Here's a good article about how third party developers were caught off guard by the Wii's success and are desperately trying to play catch up. The article is primarily about EA, but mentions some others as well.
Some intersting quotes:
"Those companies are backtracking,'' said Anthony Gikas, an analyst at Piper Jaffray & Co. in Minneapolis. "They're going to need to get their best-branded product on that platform. That will take a good nine to 12 months.''Nintendo's lead will widen, pressuring companies even more. Researcher IDC predicts Nintendo will ship 16.1 million players this year, outpacing Microsoft's 9.87 million Xbox 360s and Sony's 9.1 million PlayStation 3s.With six months to go before Wii's release and games requiring a year or more to develop, publishers knew they were in trouble."It's not really a bet anymore,'' he said. "It's a viable system that's going to make us money.''