I mean, sure, if someone goes and plays Rock Band with a goal of understanding the game's mechanics and getting very good at it, they might be a hardcore gamer.
If you consider playing a significant variety of games as a necessity for being "hardcore", then they may not be.
Most games are deep and forgiving enough that they can be played both in a casual and hardcore way. Some aren't, however.
I mean, do you really think that Cooking Mama and Carnival Games and... whatever else can really be played in a hardcore way?
Also, no person neatly fits into either category of "hardcore" or "casual". I'm sure there are plenty of hardcore gamers who are quite happy to mash buttons and watch the pretty effects in Marvel vs Capcom 3.
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[NO BARKLEY NO PEACE]