In gaming, the term "hardcore" isn't defined the same way it is in other fields.
For example, a hardcore football fan will follow every college team; professional team; and possibly even the local high school teams. They can tell you the names of all the coaches and team owners for every team for every year of the sport's existence. They buy season tickets for their favorite team and every piece of paraphernalia available. They are obsessive.
This is usually true for the term "hardcore" in everything......except gaming.
Typically, "hardcore gamers" are self-proclaimed as such. They are often teenagers and they usually stick to one platform (be it PC or console). They have favorite genres of games; those they deem to be "hardcore games." Which is actually pretty funny. THERE CAN BE NO SUCH THING AS A "HARDCORE GAME." It doesn't exist. How can a GAME be "hardcore?"
Here's the thing, if you want to be considered a "hardcore" gamer, you would have to be obsessed about EVERY aspect of gaming. You would have to own every console ever made; play every game possible; absorb every minutia of information available on gaming; etc.. Your life would be gaming.
It is NOT a good thing to be "hardcore" about any hobby.
My End of 2008 Hardware Predictions (console only):
Wii : 50 million
360: 28 million
PS3: 24 million
These predictions were made on January 3rd and won't be revised