The comparison with store brands doesn't really work because Costco and Sam's and Target don't invite third-party sellers to build their businesses on what amounts to sharecropped shelf space. Procter & Gamble and Berkshire Hathaway can hold their own in any negotiations with Costco and Amazon. For small businesses, the situation is more like the complaints we always hear about Apple's app store, where the company buys or builds their own first-party competitors in categories that prove unexpectedly successful.

Dirty pool, but legal enough... at least as long as you (a) don't hold a monopoly on distribution, or aspire to do so; and (b) didn't just get back from Washington, DC where you told Congress that you didn't do this. Both of these factors are problematic with Amazon, IMO. It's true that they don't hold a monopoly on distribution, technically speaking, but where else are third-party sellers supposed to turn?