I only just updated it, the message said something about Wii discs forcing an update.
I'll look into it.
EDIT: From Wikipedia:
Quote:
* Disc Channel updated to display "Wii SYSTEM UPDATE" if the game currently inserted into the Wii contains a Wii Menu/Channel update (required to play)[1]
* Disc Channel graphics on the Wii menu and channel preview for GameCube discs has been changed