Of course, the fact that the threshold has to be so precise is because that's the rules, not because of anything related to aviation. That's a human-enforced quality. A threshold at 100 probably has about one significant figure, sometimes less.
Well, not necessarily. The "and repeatable" can be quite a constraint.
Imagine three redundant systems on a plane that want to compute the same from the same input array (and then check whether they all agree). You want to implement this, and figure that (since there's a lot of data) it makes sense to parallelize the sum. Each thread sums some part and then in the end you accumulate the per-thread results. No race conditions, clean parallelization. And suddenly, warning lights go off, because the redundant systems computed different results. Why? Different thread team assignments may lead to different summation orders and different results, because floating point addition is not associative.
More generally, whenever you want fully reproducible results (like "the bits hash to the same value"), you need to take care of these kinds of "irrelevant" problems.
