In some situations I agree you can get a rough and ready sense of one curve or other. Certain types of auctions, and order books for financial markets are examples (though I think your link is broken!).

Even with order books though, they just provide point-in-time snapshots. It’s well-known that buyers will get a better fill than what’s shown in the book if they break their order up over time: that’s why it’s normally to trade VWAP.

These are definitely the exception rather than the rule. I work for a financial services firm and I can confidently say we have no idea what would happen to demand if we cut our fees.