After making my opinion known about this touchy subject on my recent podcast, I figured I should shore up that opinion with some reasoning.
First, this is Raph's Post that started the discussion.
The question is, where does a player sit on the continuum between casual and hardcore? I think you can best figure this out by looking at the player's emotional investment in the game in question. This is very close to Damion Schubert's definition.
If you establish the casual-hardcore continuum only in terms of numbers of hours played, you misrepresent players who would play more, but are prevented from playing (because of illness, parents, social pressure, etc.). Number of hours played is a good indicator, but it's not the whole story.
If you base the continuum on how failure-tolerant a player is, you misrepresent players who play a game with great intensity, but who don't happen to take as many risks. For example, much ado is made about care bears vs. PVP'ers. Having watched players at various points on the care bear - player killer axis, I think it's safe to say that they're looking for different sorts of emotions, but the players' actual level of emotional investment is not necessarily affected by one play style or the other.
If you label players based on what kinds of games they play, you misrepresent players who are heavily engaged in games that just happen to be given the "casual" label. I agree with Raph in that the "mass market" label might be better here.
What we are left with as an accurate measure is the level that players feel like they are emotionally invested or engaged with a game. People who are heavily invested in a game are hardcore players, and those less heavily invested are casual players. Regular players fall somewhere in-between.