That is not always true. When the iPhone 6 started to "bend" unexpectedly, Apple denied the problem completely and refused replacements until they started to receive bad press for it. Even after that, they didn't acknowledge the problem at all, and claimed that only a handful of devices were affected when in-fact a substantial percentage were. Same thing kind of happened this year with the phone casings expanding.

If a significant hardware issue presents on the iPhone X, Apple will most likely try to delay or deny any fixes or replacements, especially because they are under a struggle to meet the demand as it is.