Hardcore used to be gamers and not games. So, people like those guys in The King of Kong who competed for the highest score in the world in Donkey Kong they are hardcore gamers. Athenewins is a hardcore gamer after setting all the records in World of Warcraft. If someone is playing Wii Sports or Wii Fit hours every day and unbeatable at the games or in how fit they've become, then they are hardcore Wii Fit and Wii Sports gamers.
Now the term core itself the way it is being used is a rather new phenomena that stems basically just from last E3 when Nintendo issued a statement that they were going to be showing off lots of games for the core gamer. And gamers and Nintendo must have had a different opinion on what that term meant. Gamers were expecting a new Kid Icarus, Mario, Zelda, or Earthbound to be demonstrated, and what they got instead was Animal Crossing which does have some appeal to core gamers and Wii Music which was supposably more for everybody (and in Nintendo's opinion, everybody = the core gamer).
Heavens to Murgatoids.
