ESRB's ratings list. Zombies Ate My Neighbors, Teenage Mutant Ninja Turtles 2: The Arcade Game, and Duck Hunt are no longer listed for the Wii on the rating organization's website.
The most obvious interpretation is that these games are no longer planned for release on the Wii. But why would the ESRB remove the ratings? Even if Nintendo (or Konami) decided that they were definitely not going to release the game, ever, the content rating would still be valid. And we find it very hard to believe that Duck Hunt, a game that is pretty much synonymous with Nintendo nostalgia, has been permanently banished from the VC.