innerdude
Legend
Really, only three kinds of systems exist:
Hit points; When X points of damage cumulate, Y happens
Damage steps: If damage is X+, level Y occurs; strictly speaking, damage doesn't cumulate. (In pure systems, lesser damage steps usually provide a bonus to achieving higher damage steps.)
Damage saves: Make a save vs Damage to avoid effect.
pretty much everything else is combinations of these.
Any cumulating damage step system is essentially a hybrid of pure damage steps and hit points.
WEG Star Wars, WWG's Storyteller, and several others use Hit Points combined with damage steps with hit points, in that if you've been hit for X-level damage, and step X is full, fill step X+1.
Damage saves aren't all that common, and most of the ones I've seen (about 5 different systems, but the names don't come to mind). More commonly, they are mixed with HP to avoid certain effects: GURPS combines them with Hit Points, as does Feng Shui. WEG Star Wars combines them with Damage Steps... by using them to determine which damage step is taken (and combines with HP because they cumulate).
Marvel Heroic uses damage saves and cumulative damage steps, too.
This is a coherent, concise summary. Nicely stated.
Savage Worlds is a combination of options 2 + 3 ---- Hit X damage in a single attack to move up a damage step. The player has the option of spending a healing surge / "hero pool" to make a vigor check (i.e., CON save) to negate the damage.
It's clear now that the issue I'm having is that SW is that it's combining damage step + damage save with no hit points to be found. In light of this basic modeling, hit points are the only way to do "accumulation" type damage without simply setting a damage step threshold.
The One Ring is hitpoints + damage step, albeit only a single, binary damage step (wounded vs. not wounded).