This maneuver, Exhausting Strike, is meant to cause the Exhausted condition, so no that's not right, but upon further examination of the fatigue rules you are correct that the sentence outlining the effects in combination with Wearying Stance doesn't make much sense. This is because nothing happens to an Exhausted creature that becomes Exhausted again.
My suggestion for the wording of Wearying Strike and Wearying Stance, and it's one that's supported by the Intimidating Strike feat:
"This maneuver cannot be used to increase a creature's condition beyond Fatigued."
It's a slight nerf to them both, but a rather justifiable one if you ask me. I always thought that double Exhausting somebody forced a save against falling unconscious, but I don't know where I got that notion because it's not in the SRD anywhere.