The distinction between casual and hardcore does not come from the games themselves, but from the players.
You give an hardcore player the most casual game there is and he will still play it as if it were a hardcore game, fiercely competitive, min-maxing every aspect, etc.
Chess for example is a pretty good casual game, rules are simple enough to learn relatively fast, a match is short enough to kill some time with a friend if you have nothing else to do, etc. Yet, there are people who dedicate their lives to the game and still won't be able to learn every aspect of it.
In my opinion, a game is a game. There is no distinction between a casual and a hardcore game. If the game is well designed, it caters to both audiences at the same time very successfully.