That's almost a convincing argument, but you missed something - a corporate store means a complete monopoly on the product, and the price is 100% fixed. Think: Apple.
That does not mirror a grocery store. Sure, the price of a can of beans is fixed, but only at that store. If you don't like the price for that exact can of beans, you can try several others, and often can do better.
I do get your point about the secrecy though - although for the most part, even though prices are openly posted everywhere, they are de-facto secret because you can't get the information. You don't know how much a can of beans costs at all stores right now. You don't know how much I paid for it yesterday. It's still secretive, though open.