As far as I'm concerned, hardcore gaming is beating the NES Battletoads without dying. Hardcore has nothing to do with graphics. "Hardcore" gamers are still playing games like Ninja Gaiden (the NES one kids) and trying to get an even higher score on Donkey Kong Jr. They're the people Full-Comboing insane songs on DDR and typing in attack commands by hand on their favorite MUD.
What the Wii doesn't appeal to is gamers with a ton of money that want to play Halo while getting wasted with friends. "Hardcore" gamers don't care about graphics, they recognize that gaming greatness is not graphics-driven. To the industry however, "hardcore" means "have lots of money to squeeze out 7 more fps;" and they're right, to them, the Wii does not appeal.