Luigi was a "secret" charater in the first 2 (He was pretty hard in both games too!)
I think with the massive amount of side stories and such(targets, whatever) there has to be alot of secret charaters. I think Brawl may be as much as 50/50 secret and starting roster.
End of 2009 Predictions (Set, January 1st 2009)
Wii- 72 million 3rd Year Peak, better slate of releases
360- 37 million Should trend down slightly after 3rd year peak
PS3- 29 million Sales should pick up next year, 3rd year peak and price cut