Discussing casual vs hardcore without defining the context is pointless.
Some measure hardcore in terms of how much skill is required, others in how much time is invested and others in how approachable a game is.
SHMUPs (Ikaruga, Contra, Raiden) are very approachable games, yet are considered hardcore (skill required).
MMOs are considered hardcore because of the time required to reach the endgame, and be proficient in it.
Simulators (milsims, flightsims), for the most part, can be considered hardcore because of the steep leaning curve, e.g. approachability.
There are all these different axis of discussion, and mixing it all up will only further antagonism. A true hardcore gamer could be one that played games with hundreds of keys, for the longest time, and with uber skillxoorxs... Like a Combat Flight Sim MMO.
But wouldn't a Space Invaders pro be considered hardcore? What about the MMO player that has all the best loot, by means of grinding? And what about the guy that had to spend hours reading manuals just to be effective in his game?
Again, without context, it's a pretty moot point.