Nagoshi too =O i bet Nagoshi is the one who made the deal in the first place, hes the head of SEGA's consumer division.
Nintendo went to every 3rd party and asked what's possible I'd imagine.
Namco Bandai with their Tekken and fighting stuff which got them making Smash Bros., Tekken at launch, Pokken...
Tecmo made them a Musou game (what else!)
Sega, of course, Sonic, Sonic, Sonic
nothin' going with Capcom tough!