Examples of one retailer if you doubt me. I've no doubt other companies act in the same manner:
http://www.businessandleadership.com/leadership/item/19980-tesco-demands-six-figure-p
http://www.heenamodi.com/2008/08/18/should-we-shop-at-tesco-do-they-treat-their-suppliers-ethically/
Just browsed the first example. Nothing wrong with what Tesco is doing. They control a limited resource that a lot of suppliers want access to... It makes sense to get the most you can out of that limited resource. Suppliers don't have to pay the money if they want to... but in that case it is the cost of getting access to their customers. This is how the world works.
How do you think items get into a retail store? As a retail buyer many years ago, I can tell you there are many different aspects to the negotiation and it depends on a lot of factors. Some stores may charge money for slots, other stores may require advertising coop spends, others may depend other concessions.
The problem is there are laws in many places that limit selling things at a discount outside of volume that makes the whole retail supply chain dicey. So there are other ways to make those decisions besides just demanding the lowest cost of goods. Not to mention that is accounted for entirely differently.
If you had a store with a slot for 20 items and 50 people wanted those 20 slots, how would you decide who gets the slots? What if the 5 in contention for the last spot were all fairly similar in cost and product?