Just because there are a lot of casual games on the system doesn't mean it can't be "hard core". There is a hell of a lot of trash available for the PC, yet I'd still consider that is a "hard core" gaming platform.
I don't really agree with the clan/communication definition either. I'm sure it's probably a lot of fun to shout "boom head shot" to your clan mates when you blow someone's head off from the oppositions team. I don't see how that's any more "hard core" then solving an incredibly difficult puzzle in Zack and Wiki though.
'09 looks to be shaping up for a great year for Wii owners. With all the solid third party efforts already released this year and many more to come. Not to mention the Wii Motion Plus sports gaming that can only be described as incredible according to IGN.