If your wii is on the original firmware, any game released after the first mandatory update would require a system update! Thus if someone hasn't played a wii game since 4.2, they will need an update to play Zelda because it is 4.3. Its just a Cover Your A$$ type of thing. All of those red boxes are put in there by the legal team. They dont want someone to raise hell and sue because they dont want to update their wii at all and when they try to play "X" game they purchased it wont work without an update. Without this warning (among others), people would be more likely to at least attempt if not win a lawsuit based on the fact that "they were not informed that they would have to modify their original purchase in order to play newer software."
It is possible that Zelda will require a new update, but I think we would have heard something by now. In all likely hood the news of a new update would have trickled down from some disgruntled developers (even third party developers would know if a new update is coming, as they would need this knowledge for their own projects).
Edit: Damn! daniekraak beat me to my point....!!