I and many other users have had several channels deleted during the update I can now safely confirm why. During the update process, the Wii checks to see if enough space is present to download the new system menu and IOS files. Since it is downloaded before it is installed, a lot of space is required. The biggest channels are therefore delete to allow around 1000 blocks of free space. I can not confirm, however, that the game saves for some of these channels were also deleted, since I can only confirm that it has happened to me.