When did Dell stop honoring the warranty for chassis failure?

The hinges on my 2-in-1 failed while switching to the tablet configuration. Unit wasn't dropped or anything like that, just old and opened and closed a lot. No big deal, sent it in for warranty repair since it's just cheap hinges that failed on a cheap laptop. Surprise! Just went three rounds with "support" after which they refused service because the device is "damaged". No kidding it's damaged, the hinges failed.

Any idea when Dell decided that the chassis of a laptop wasn't covered by warranty?