The idea that there is a difference between casual and hardcore games. All those terms describes is the mindset about those games.
It is possible to play a game like Dead Rising, Left 4 dead, Fallout 3, or Halo once in a while for 15 to 45 minutes at a time and walk away from it for 6 months. It's been atleast that long since I played Fallout 3. Furthermore, it is possible to play games like Dance Dance Revolution, Cooking Mama, Rock Band, and Peggle for hours on end een to the detriment of food, sleep and work.
Heck, fighting games are often called hardcore games, but they are the very definition of casual. Put in your quarter, choose your favorite character, play the game until you lose, then either continue or walk away.