It’s because there’s been changes to the USB code in libogc. These changes make more USB devices work, so I release a new forwarder with these new changes compiled in. If the channel already works for you, there’s no need to update. If the channel doesn’t, then it’s more likely that it will on the newer version.
I’m hoping the changes in libogc will stabilize soon so that I can stop releasing a new channel every time! 😉