What actually happens is widely debated, never acknowledged by anyone "official". The anecdotal evidence is there, as are some obvious differences like the plastic drain valves on the Rheem water heaters.
The classic example I point to is Buck Knives. Walmart wanted Buck knives. Buck wanted to sell to walmart, because it is hard to ignore that potential volume of sales. Walmart demands a price point which Buck cannot possibly achieve. RESULT: Buck opened a factory in China. Those knives are sold ONLY at walmart. Is it the same knife you buy at a sporting goods store? You decide.
In answer to your question about who refused to knuckle under: you will find the answer if you find a product which is NOT sold at wm/hd/lowes/target