Actually playing the game won't be the first thing you do when you put the disc in your Wii.
There are probably plenty of people out there putting Metroid Prime 3: Corruption into their Wii for the first time and noticing a strange message. The first time you go to the disc channel a message will come up asking you to install a system update directly from the disc before playing. Thankfully this update happens very quickly so it won't delay the experience too much.
It's currently unclear what the update does exactly. There could be new Prime specific features or this could just be a way of getting already released system updates out to the people that don't have their Wii connected to the internet. We'll bring you any new details that come up as we become aware of them.