One basic exception is less about lack of trust, and more about lack of consistency.
Players have to have some ability to guess what might succeed, and how likely it is to succeed, or they lack the ability to make informed choices. The more things are ensconced in rules they know and can depend on, the better they can make those choices. The more things are handled by the whim of the GM, the more shaky those decisions become.
Now, a GM who has a sense or talent for making those calls consistently, the more the GM is like a rulebook the player can learn. The more inconsistent or arbitrary the GM is, the less the players can depend on the results.
Some players like to have more of that consistency, and they will prefer rulesets with more definition, others don't find it as important.