I would think theres more to this story, not on your side but thiers. I could see the potential for a concrete line in the sand from them.
The possibility exists some other scenario in their past made them take this stance. They bend the rules a little for another customer, who in turn wants it bent further on a second job and before you know it the 144 price break is awarded to 100 pc jobs.
At any price break point on any product there will always be circumstances that do not make sense. Obviously it costs them X to set the job up and they bury X in a small run or disperse X in a larger run.
Sorry bud, but your view on their policy really means squat. As a business man/woman you should use the advice above: take the 144, throw your customer a bone, be a hero, save the money and move on. If the customer really doesn't want the extras then good will them. You still come out on top.
Spend your weekly frustration allotment on something like gas prices, lol.