I totally agree with the guy above.
I would call your definition a serious raider.
I'm not hardcore, but I would call myself a serious raider.
My guild won't be a server first, but we take raiding seriously.
An I believe alot of these "Casual raiders" do take raiding seriously, and they dont like that challenge, they're just scared to call themselves hardcore.
Another way of looking at is like this, under 16's like the current system, people over 18 perfered TBC system, between 16-18 we're never sure about.
Keep in mind that's the majority I'm talking about there.
I'd also say that the majority of over 18's would perfer 25 man hard mode and 10 man easy mode.
That's just how us older folk roll.