I'll preface this with saying that my first MMO was FFXI. The way I viewed the "Hardcore" groups on my server were the ones that were constantly striving to complete content before anyone else. They played for long stretches of time in a session (8+ hours) whether it was farming ground HNMs or Sky triggers/gods. It should also go without saying that the people that comprise these groups are typically cream of the crop. You can have all the time in the world to play, but without a certain skill set you'll just keep ramming yourself into a wall.

I understand your view of what Hardcore is, and I agree with you to an extent, having played the various Diablo games over the year. I just think the definition has now more or less evolved into who has more time in their day to play.