I think “Fairness” might be a poor term for the first category, since you expressly include the use of rules to provide reasonable outcomes, even though such outcomes can very quickly become unfair. As to the use of them: I find the enjoyment in RPGs as a player to be in making moment-to-moment decisions as the character and seeing the effects, and having an engine that spits out reasonable outcomes is an easy way to make those decisions informed and meaningful.