Well, Johnny's always been the country musician for people who hate country music and you have to admit the timing was perfect- the video was shot 7 months before Johnny died (and only 3 months before June died) and was unabashedly nostalgic, featuring archival shots and shots from "The House of Cash" (Johnny's former home which was turned into a modest version of Graceland I guess). Anyway, I don't see a problem with any of it- the cover was good, the video was tasteful and if Johnny can convert folks to country by covering a 90's classic with a universally relatable theme (since cliched, corny, old fashioned lyrics seem to be what turns a lot of folks off country), I say great, hopefully they'll check out some Townes Van Zandt.
So wait, Reznor sounds like he's trying to sound like a teenager to you? I don't get that at all. Again, he over-emotes but not any more than the other 90's whinys you mentioned (and the lyrical content of his songs often arguably makes over-emoting more appropriate than it does for those other 3 singers) and he's technically a pretty good singer. Listen to that falsetto in "Heresy" and ask yourself if Cobain, Corgan or Vedder could have pulled that off. And as Trung has pointed out more times than any of us care to remember, all male singers can be judged purely on the strength of their falsetto