It's not unusual, I work with e-commerce merchants and often their suppliers will insist that they cannot reduce the price of a product beyond say 10% of the RRP they specify, even in a clearance sale. Certain cycle manufactures in particular do this. It's because they want to maintain their brand as a premium brand, and don't want their products to be seen going cheap. And if you break the rule then they WILL cut you off. That's not to say the rules never get broken of course!
Andy
Andy