People who play CoD and Madden only are more "casual" gamers. Hardcore games are people who enjoy all different kind of games. People that will buy several games, not just the 1 or 2 games every year.
That's how I'd define it as well.
Hardcore gamer is someone who buys and plays a lot of games in a lot of different genres. It's the gaming equivalent of a movie buff. Someone who just goes and sees (or rents) the big blockbuster films isn't a movie buff. A movie buff sees those, plus the award nominees and foreign films and indie films etc.
Someone who just plays a ton of COD or WoW or Madden is just a serious/hardcore player of those games, not a hardcore gamer overall.
I like the distinction that article I mentioned earlier made.
Hardcore=the above.
Softcore=the CoD/madden type who may game a lot, but have limited genre interests and don't buy nearly as many games
Casuals=people playing facebook/phone games, maybe Wii sports and some casual stuff on a console if their spouse or kids have one etc.\
Softcores are the biggest chunk of the market, but the article argued that in terms of what console they buy they tend to follow what the hardcore buy. The hardcore early adopt, the softcore play next gen games first at their hardcore friends' places and are more likely to buy whatever that friend is gaming most on so they can play online with them, borrow games etc.
Last gen it wasn't just the softcore that helped MS when in the US. It was that Sony alienated the hardcore early adopters with the stupid high price as a result of a non-gaming feature (bluray movie playback), bad PR from comments that people would work a second job to afford one and so on. They eventually got back neck in neck by catering more to hardcore gamers, putting out a wide variety of exclusives, launching PS+ etc.
This time it's gone the other way as MS pissed off hardcore gamers with the DRM stuff, and being $100 more due to having a non-gaming feature (Kinect) forced in. Well, I guess it is used in games, but not the type of games hardcore gamers play so still a wasted expense for them. Especially when the competition is $100 less, more powerful and running games at higher FPS and resolutions (and hardcore gamers care a lot more about that stuff than softcores) and doing more to cater to them directly.