I think that Apple is full of **** concerning the whole no signature thing. When it comes to having to type in your pin or sign for something, I believe that stores and credit card companies set those requirements.
Correct, it's up to merchants, credit card schemes and banks.
However, note that Apple itself has never claimed that TouchId got rid of current signature / PIN requirements.
That idea was made up by people who do not understand the way US credit / debit card purchases currently work.
Sure, Apple's videos never showed it happening, because that would make Apple Pay seem less magical. But they weren't lying... they simply chose situations where a challenge wouldn't occur. Apple marketing always tells a verifiable truth. They just avoid showing the less magical cases.