Such a system will surely work; it does work, after all, in 3.5.
Therefore I can merely explain why I did not use the Fort/Ref/Will save system in ACKS.
I think it made concrete what is necessarily abstract. To me the classic example of a saving throw is the example of a hero fighting a zombie in any George Romero horror movie. Let’s compare two different models.
3.5E: "If the zombie successfully hits its target, the target must make a Fort Save DC 25. If the saving throw fails, the target is infected and will become a zombie in 1d6 hours.
ACKS: "If the zombie successfully hits its target, the target must make a saving throw versus Death. If the saving throw fails, the target is infected and will become a zombie in 1d6 hours.
Note how in the 3.5E model, the zombie infection requires a Fortitude Save. That’s how 3.5E models diseases and poisons: You’ve been exposed, but your toughness and high Constitution might save.
Yet in Romero movies, a hero does not survive the zombie apocalypse by shrugging off the infection (a Fort save); no, anyone who is bitten is inevitably infected. Instead the hero survives the zombie apocalypse by never getting bitten at all! He might not get bitten because…
- He is very lucky
- At the last minute the zombie’s teeth bit on his thick leather glove and didn’t break the skin
- He maneuvered in such a way that the zombie was able to body-slam him but not to bite him
How the hero avoids getting bitten will depend on the type of hero he is. All of these abstractly factored into “saving throw v. Death”.
(Also note that the hero will still “lose hp” when fighting a zombie - thrown into the wall, knocked sideways, etc. The monster’s attack throw determines whether the hero takes damage; the hero’s saving throw determines whether his skin was broken by the bite.)
Thus, the seemingly arbitrary difference in the game mechanics actually models a totally different in-game reality. In one system, the hero was bit but somehow not infected. In the other system the hero was hit but not bit, for a reason that is defined by the Judge in light of the situation and character.
Perhaps a system of “single save with ability score modifiers” could work if the Judge requires that the player explain how his character is avoiding the threat and then uses the ability score which is most appropriate. (“I try to roll away before it can bite me!”-DEX bonus; “My thick-as-leather Dwarven hide canna be pierced by no girly elf-bite” - CON bonus).