UPDATE - The game has been re-added to the Wii Shop Channel.
Here's a really strange one for you. While Donkey Kong Country 2 and 3 are still available on the Wii Shop Channel, it seems that the original title has up and left the service. No reason behind the removal and no word on whether it will be back or not. I wonder why Nintendo would yank one of their own games. Thanks to KingBroly for the heads up!