This is just wrong - see the Hal Finney attack. Basically, an attacker can pre-mine a block with the double-spent coin in it but not announce it. Once an attacker spends the coin and gets something of value, they can immediately announce their block, pay the coin to themselves instead, and keep the goods.

It's true that it would be hard to get a lot of value this way, but it's still the case that the person accepting the payment must be wary of the possibility and, as you say, be able to reverse the transaction if the coin ends up double-spent.