>(Which is the threshold for success rolls in, uhhh... everything. Isn't it?)

100 isn't the threshold for RT infliction in a number of maneuvers. Some critters are actually guaranteed to inflict RT however badly they fail at the main aim of their maneuver (which in the case of feint is the stance forcing, not the RT infliction, you don't get your stance forced until 101).

Locks and traps is another system which inflicts penalties on the target at rolls of under 100. An 83 makes the lock easier to pick. Think of that feint roll as like a critter modding you down.

Also, unless I'm mistaken, I believe feint has a partial success on 80-99 roles.