The whole way the parental controls work is that the game has its rating programmed into it, and the console reads that rating.
Gamecube games didn't have the rating programmed in, so the Wii can't read it from the game (although, if Nintendo wanted to, they could just write a fancy program for the Wii to recognize certain codes in every single GCN game, enabling it to know what the game is, then have the program know whether that game is M-rated or not. But that'd be a complicated program to put together, and really a waste of time).
Either way, VC games are obtained via the Internet, which makes 'em much easier to write in the same parental-control code that Wii games use.
It wouldn't even require a firmware update. The only reason M-rated games haven't released on VC yet is because really, the only M-rated games that would be worth putting on it are on N64, and they're few and far between.
SW-5120-1900-6153
