On the Wii the NANDLoader is included in a title's main binary ( app, in dol format). It is usually the first text section and should always be written to 0x80003400 (PowerPC reset vector)[check]. The NANDLoader should initialize the PowerPC and jump to the binary's main function.
On the vWii, because the Espresso only boots Ancast Images, the NANDLoader must be signed. Nintendo solved this by adding title 1-512 as a NANDLoader. When launching a title other than the System Menu, IOS will start one of these NANDLoaders to initialize the PowerPC. These NANDLoaders in turn load the title's main binary and jump straight to it's entrypoint, skipping the title's NANDLoader which is included in title's binary.
Because the Homebrew Channel had its own NANDLoader, fail0verflow never bothered to set an entrypoint, as the custom NANDLoader knew where to jump. This resulted in the channel initially not being compatible with vWii. fail0verflow solved this by adding an entrypoint to the dol header. This resulted in the channel's NANDLoader being run on the Wii, and skipped in vWii.