Honestly, it's a term the Sony fanboys used to try and justify them not being in first place and to piss off the Wii fan/boys.
It's funny how any game that hits the Wii is automatically coined a "Casual" game. Then a game like Little Big Planet comes out and it is coined a huge "Hardcore" game (and of course people go into racist mode when it gets delayed by a week, but that's another story).
Point is, if Little Big Planet was a Wii title (of course with not as good graphics, but still everything else), it would be dubbed a casual game, yet since it's on the PS3, it's Hardcore.
Don't get me wrong, I'm not saying the term "Hardcore" doesn't exist, I think it does exist, however that is entirely subjective in a lot of cases. I definetly do think the Wii series games are casual, but that doesn't mean they aren't as bad, it just means that they appeal to a crowd that isn't as familiar with gaming as the more "Hardcore" gamers are. Hell, I have a blast playing Wii Sports with my friends (and I consider myself a hardcore gamer).
I do enjoy hardcore games like SSBB, MKWii, Twilight Princess, SMG, Halo 3, MGS4, CoD4, many more.
Anyways, that's my 2 cents.
