Wii won't have as many blockbusters next year as it did this year, but that's okay. Third party support will definitely increase, and the blockbusters aren't going to disappear after a limited time. They'll be on the shelves helping the system sell until more blockbusters come in 2009.
(Not to mention that games like Wii Fit and Wii Music have a ton of blockbuster potential if Wii Sports is any indication).