Speaking from what I have experienced, it depends entirely on the person, not the conference (NPC/NIC/NPHC). I've got co-workers who have said "I was a (insert letters here) from the NPHC. It's not just NPC/NIC people who say it in the past tense. I also have co-workers who have said "Oh that was back in college, I don't do that anymore."
It's a personal preference one way or the other. Every organization has members who are "financial", members who give time, those who look at it as a college experience only, or those who give $$ and time. Sure we could all make generalizations based upon the type of organization it is, but we all have international/national officers and alum advisers, so obviously some people live the lifetime commitment.
ETA: You can't force alums to be active, and we all know of some who it would be better if maybe they had other things going on in their lives as well.
