> Yes, and the same reasoning would apply to folks suggesting that employers routinely are open to negotiation.

No, it wouldn't, because employers have a strong incentive to hide salary band violations, while employees have a strong incentive to discover when negotiations are possible.

> it strikes me as an extraordinary to claim successfully negotiating higher-than-average wages is typical.

Then you should probably go talk to somebody who made that claim. But it's a nonsensical claim, so my guess is not many would be making it.