Pretty much anyone can pick up Brawl and play it and have fun. So is it casual?
There are plenty of people that play the SSB series at such a level that every button press is thought out ahead of time and a single slip-up can mean a KO. So is it hardcore?
Brawl(and most fighters really) is a great example that games are neither hardcore nor casual. It's such a success because players CAN play it casually with their friends, but it also has the depth to play it in a hardcore manner.
It seems I missed a point in the OP, but Zizzla and Smashchu totally nailed it. For Nintendo "core" gamers are those that buy and play their core franchises, which are pretty much any IP before the DS/Wii such as Mario, Zelda, Metroid, Kirby, etc. Because of this Brawl most definitely is a Core Nintendo game as it features the stars from all their core franchises.
EDIT: The casual/hardcore thing goes for every other game mentioned in this thread.
@Esa: Zelda certainly is easily accessible to people that want to play it casually. There's also those that play it in a hardcore manner. Either by getting every single thing possible or collecting as few things as possible while beating the game(3 heart runs) and there's also speed runs.
