Nintendo-centric site The Wiire
sifted through the Q & A in the Wii Shop Channel and discovered an interesting portion that explained the Update button, where you can download "enhancements" for a game.
It is unknown what enhancements there might be. The Q&A mentions that the updates would be provided free of charge, but that doesn't rule out other charged microtransactions. Likely the update feature exists to fix glitches; however, graphical improvements and online capabilities would be a nice touch. Who wouldn't want to play Mario Kart
We've contacted our Nintendo rep and will let you know what we learn.