It looks like the joke's got a hint of truth! Or at least it was Nintendo's plan back in 2006: http://uk.wii.ign.com/articles/726/726749p1.html
Excerpt:
"The machine is based on GC," said Miyamoto. "We'll be upgrading the development tools, but GameCube code can be used for the most part as is. In that sense, I believe that it would be good to remake GameCube games for Wii, and that some titles would become better with the change to the Wii remote controller."
Best of all, Miyamoto envisages any such remakes will retail at a much lower price to their 'Cube originals, and may even help bring third party support to the system. "Even now," continued Miyamoto, "[GameCube titles] are sold at used shops, so we don't feel we could sell them for full price. However, development costs have been taken care of, so we could probably sell them at a more accessible price. If we make it so that such GC to Wii remakes can be produced quickly, it's possible that many titles will also be released from third parties."
