Cash uses his voice as an instrument to convey that regret. He had a wonderful, weary voice at the end of his life.
The lyrics of Hurt are pretty silly and they are whiny as hell.
Cash is able to recontextualize them because, well, he's a far more gifted singer.
Agreed that he's a more gifted singer, but no, the lyrics are the same, and the context of them doesn't change, because their coming from Cash.
While Reznor might not have had as long a battle with life as Cash, he still had struggles.
I'm saying Reznor is a poseur.
So, no, Reznor was not just pretending.
So, IYO, Cash is able to take everything about the song, which sucks, and make it good, because he was a grizzled dude. Gotcha