The reason we don't discount subscriptions or offer special weapons for HC is because too many would join HC just for that reason and we'd have to track activity etc... the people we need in HC are players with a volunteer spirit, players that want to make the game better for their fellow players just because it improves their game.
If you base the discount on activity like moving units you'll get some clowns that come in move 5 brigades at random screwing up all measure of gameplay just to fill their quota... nightmare
The only people that will join and stay in the face of adversity are players that genuinely want to help their team, it isn't a perfect system by any means but until we shift to a town based supply it is what it is.
I had fun with it, I was in HC for years, I was CinC for 2 campaigns, I had a full HC roster and that made it easier. I salute the guys who do it now and stick with it thick or thin