The fact is that people know there are TONS of shovelware on the Wii. People do buy most games coming from Ninty - because Nintendo has a solid reputation about their quality games - so this is why most of third party publishers do have problems to sell their games.
Third party should put more promotion on their products and suggest bundles with a higher retail price. Nintendo should also make some moves to help third party. I guess the are reorganizing in intern to prepare themselves for the future.