Might be wrong, but I think that's been pushed in game design (particularly around the mmorpg area) that more difficulty of play aught to equal more reward.
The thing is more reward for more 'difficulty' (where that difficulty is just higher enemy stats) can even be easier than before. Say instead the monster that would normally inflict on average 10 damage over a fight to your 30 hit points and give 100 gold, inflicts 20 points on average and gives 200 gold. You can then go and heal. Well this is easier! What's the difference between healing off the damage? None and you got more gold? It's just easier than before! The only thing that could change that is a spike in damage (and dice pools tend to average out).
If reward actually tracked to higher difficulty perfectly, then unless there is spiking damage, there is no point, it would always be effectively the exact same difficulty as before, but with higher numbers (though it would cut down on grind, granted!).
Difficulty has to always be incommensurate to reward otherwise difficulty has not been raised. The only reward higher difficulty can really impart and still be higher difficulty, is the knowledge you did it on a harder difficulty.