I don't think they made any promise? The problem for them is that they really cannot tell how the phone was bent. Was it from everyday use? Was it from everyday misuse? Or was it done on purpose?

If they flat out and say they would replace all bent phones, it would open up a flood gate. There will be hundreds or thousands of people trying to bend the phone just to see if they could do it.. and if it bent, get a new one!