All I can say is, your save files are temporary. The console's gonna die or the memory card's gonna die (even official ones). Might be twenty years, might be two. I wish save files weren't occasionally tied to consoles. I'd understand the angle of "we don't want you to cheat by loading up someone else's save" or "your save may contain personal information that would be a breach of privacy to copy over". But if it's just for the purpose of backup, then let us back it up! I suppose then they'd counter with something like "it's illegal to copy a cartridge/CD because it might be used for distribution, so too it should be illegal to copy someone's saved games because they may be distributed".
You can't move data for WiFi games like Smash Bros. Brawl, I guess because of network settings. Maybe it includes username/password to authorize the Internet connection, or maybe it's that the info wouldn't apply if used on a console that doesn't use the same internet connection. They can't just strip out the network data, no, they have to prevent the whole enchilada of Brawl data from being moved. You can't move data for some non-Wifi/GameCube games like F-Zero GX. Why? I don't know, probably to prevent cheating. Which sucks when said save game files are by far the biggest files. And
this topic for the Xbox360/PS3 version of Rock Band suggests you can't move saves because downloadable songs are part of that save. If you used someone else's save, you'd be able to play songs that you didn't pay for. But then, apparently there's a one-time process you can use to transfer all data from an old hard drive to a new hard drive... why can't Wii have that?
I wish Nintendo would be straightforward and have an easy-to-find page explaining exactly why some save files can't be moved. I haven't read the Wii manual, but I don't think they say anything about immovable files. And if they do, they probably say "it can't be moved because we say so". People should know going in whether there will be any restrictions on saves. At least the box says how many blocks a save is, thank goodness for that, but they need to supply more info.
This thread mentions somewhere a possible cause for why GameCube memory cards might get corrupted while in the Wii: the Wii gets warm in standby mode, and warmer when running. Heat rises. If you have your Wii in the vertical position, then the memory cards are at the top (right where the heat's going), so they're getting all this heat and possibly dying off. You can try keeping the Wii in the horizontal position (I prefer that so I don't have to guess which side to insert the CD). Oh, and general advice for any game console: have it in a well-ventilated area.