One of those things that's there if you need it. Wisdom, primarily, controls some of the more important "Modern" skills, like Treat Injury, and they used it to control Advanced Firearms Prof.
You could, in a modern game of gunbunnies and no investigation, probably get away with tanking wisdom and not noticing it in failed Will saves.
I will say that I like that you get advancement in the save ANYWAY, just in case you DO use FX. I remember playing Alternity, where everything was a skill, including the cognate to d20's Will save. Not taking ranks in the skill was fine, never noticed it, right up until something that called for that roll came up and everybody went: "oh ... crap". D20M, you end up with some minimum proficiency with all of the saves as time goes on.
--fje