I disagree, actually. I think it should effect all creatures. But I think the threshhold of what constitutes “completely annihilation” damage should obviously increase significantly the larger (or, more simply, higher health) a creature is.
I’m fine with a 20-ton death-machine turning a bear into fine red paste, or at least leaving very few gibs behind. Or even accomplishing the same thing with a mini-nuke. but the damage capacity of standard weapons clearly shouldn’t be enough for large animals.
Basically, I think one possible way to do this would be to have an amount of “gibs” possible from overkill based on the size of the creature, and every so many points of overkill one of those gibs are removed.
Take a rabbit, say it has 5 health. (1 gib)
Take a bear, say it has 40 health. (8 gibs)
And take a hulk, say it has 80 health. (16 gibs)
You have some sort of blaster cannon weapon that deals 100 damage, and we’ll say that each 10 points of overkill beyond the initial overkill targets destroys a gib, and “overkill” is marked at dealing max-life damage with a single shot. (the details can obviously be changed, but for the purpose of this exercise)
The rabbit is obviously completely destroyed. At 5-15 points of damage, it would leave a single gib, but anything beyond that would leave nothing but a red splotch.
The bear, however, leaves a 2 gibs even at a hundred damage. That’s 60 points of overkill, meaning -6 gibs. But something, at least, is scavengeable.
The hulk, meanwhile, is overkilled by a mere 20 points. That means -2 gibs, with 14 remaining.
I think this, or something like it, would be pretty workable.