As what is "casual" and what is not, you could classify (just as said earlier) casual as a "pick up and play", meaning basically a game that doesn't require much learning to be able to play the game and that the game has a lot of things to do that don't require much skill. Good example would be GTA-series.
In the opposite is "hardcore", which games are complex and require skill to get started and to have something to do in the game. Something like Master of Orion would fit this category.
Or one way to describe would be casual= not much to do, hardcore= much to do, which seems to be the most common uses.
In general, the black and white casual-hardcore is pretty empty and doesn't tell much about anything. I think Iwata using the word "casual" was because of making (one more) difference between Wii and its competition.
In general, there are many definitions that describe games and gamers better than just "casual" and "hardcore".
Ei Kiinasti.
Eikä Japanisti.
Vaan pannaan jalalla koreasti.
Nintendo games sell only on Nintendo system.
