Like the DS before it, it appears Wii will only support title-specific friend codes for online play according to GameSpy PR folk in an interview with Falafelkid from Wii: Definitive Speculation.  When asked via email if Wii friend rosters were console specific (read: logical, usable, accessible, you know, fully operational), a representative from Nintendo's online partner replied by saying, "for the Wii friend lists are game specific." 

Were not just talking certain games that also connect to DS here (i.e. Pokemon Battle Revolution), we're talking all games.  Our team on the inside has yet to penetrate the GameSpy vault to confirm or deny the rumor, but what a rancid, partially substantiated rumor this is.  Keep hope alive?