I think the GR is just another reward system - like the points used here. It does better than the points in some areas, and worse in others. For an excellent defence of the points system, see kestas' post on the forums where TGM posted his original idea for the GRs.
Diplomacy tournaments have their own, unique reward systems too - and I'm told players turn up in them who follow personal systems different from those in the tournament. The point being, in Draug's example, if you let the little guys live, you're using a personal reward system that values this more than killing them for the 3-way draw. You made that choice because in your system, it's more rewarding than the 3-way draw, and good on you for sticking to that system - but it's useful to remember other systems may not reward it as much, or at all!
Which brings me to an interesting idea - (particularly for anyone who's ever played mansions of madness). Set up a tourney, the TD is referred to as the Keeper, and he doesn't play. He decides a reward system beforehand, per round, that is not revealed to the players. Games go on for an agreed amount of time (say 5 years), at which point he reveals his reward system, and then games continue to completion. Players progress depending on how many points they score as per the revealed reward system. The fun part is that the reward systems may be utterly ridiculous - the average sum of distances of all your units from Portugal, for example.