In the past (before the CD based consoles) Street Fighter games were released for virtually every platform but the only one that had a great controller straight out the box was the SNES. Genesis/Megadrive controls sucked and computer versions were even worse; but people would often buy a new 6 button controller just to play SF. I don't see why the Wii would be any different and most people probably own a Classic or Gamecube controller already to play their VC games.
Lets take a look at a game cube pad
Button layout - Rubbish for Street fighter or any of Capcoms punching games
D-pad - Small (my thumb covers it)and out of the way
Left analog stick - A bit to lose for fighting games
Yes I have tryed fighting games on it (Capcom vs SNK 2 EO, Soul Caliber 2) it was a bugger to do any kind of moves on that Dpad
I'd rather get it on the PS3 because I'm sure the online experience will be better. With fighting games, lag-free action is essential and Brawl's online was a joke.