Never understood why people follow this notion. All gaming consoles are for casual gaming (relax on the couch, turn on, play , stop). The number of FPS' don't make a good indicator to distinguish between "hardcore" and casual.
You are so right. It's annoying that the standard for "gamer" has become FPS players.
In my day, hardcore gamer meant you could have been into any genre, whether it be Japanese style RPGs, Japanese style shooters (I'm talking Raiden or Gunstar Heroes, not FPS), or fighting games.
The only reason why I keep a PS3 around is for stuff like Street Fighter and King of Fighters -- stuff that a "modern gamer" (i.e., gamers from the 360 era and forward) would probably call niche.
With very few exceptions, most of the heaviest gamers I know play games from almost every genre, and the more genres they play, the less likelier it is that they call themselves "hardcore".