Uh, didn't one of the later updates last year have mention of automatic updating in its EULA?
Chapter III: Updates/Changes
You understand that the Wii Console specifications and the Wii Network Service are constantly evolving and that we may update or change your Wii Console or the Wii Network Service in whole or in part, without notice to you. Such updates may be required for you to play new Wii games or continue to access the Wii Network Service. We may also upgrade, change, or terminate the Content or game software or may discontinue offering Products without notice to you.
Also sounds like they say they can brick your Wii if they want to here:
Chapter II: Unauthorized Software, Services, or Devices or Unlicensed Accessories
Your Wii Console and the Wii Network Service are not designed for use with unauthorized software, services, or devices or non-licensed accessories, and you may not use any of these with your Wii Console or the Wii Network Service. Such use may be illegal, voids any warranty, and is a breach of this agreement. Such use may also lead to injury to you or others or cause performance issues or damage to your Wii Console or the Wii Network Service. We (and our licensees and distributors) are not responsible for damage or loss caused by unauthorized software, services or devices or non-licensed accessories. We may take steps to disable or delete any unauthorized software, services or device installed in your Wii Console, for example, by detecting and disabling them through the Wii Network Service and/or game software. If we detect unauthorized software, services, or devices, your access to the Wii Network Service may be disabled and/or the Wii Console or games may be unplayable