The thing is, even if you think a Wii version wouldn't sell, making a PSP version makes even less sense.
Outside of Japan, the PSP is DEAD. Regginated.
Software sales are abysmal, and hardware sales aren't too hot either.
The point I'm trying to make is that 3rd parties frequently act like porting a game to Wii is either "impossible" and/or it wouldn't sell, yet they release many of these games for the PSP (Tekken 6 got a PSP port BTW, not that I'm asking for it) and the PSP sells jack in the west. And don't forget iPhone ports. Yeah, gamers love playing fighting games without buttons or a D-pad.