actulaly, legally, we have to be very careful with the covers. we are fortunate because we have the songwriters themselves oking everything, which opens a few legal doors, but there's still a lot to be careful of.......it's a legal minefield this covers lark, especially when the original band has a fat ass publisher/ (now) major label behind it
a good example of this would be the smiths covers album that came out a year or so back, which i'm assuming did not have the backing of the smiths. death cab for cutie were meant to be on that, because because they changed lyrics, their song coudnt be used.....
also, your johnny cash exmaple, cable sound nothing like johnny cash, therefore their cover of ring of fire was bound to sound different - whereas a lot of band who like cable, not co-incedentally, actually do sound like cable - so when they do covers that's what happens. i also think the swound one is pretty close to the original, and there's a few other on there that do too.......But unlike you, i think in context that is a very good thing.
But like i say, wait for the final thing, hopefully there'll be something on there for everyone.........and im pretty sure most of the fuss will be kicked up over the weird ones to be honest, as i reckon they are most likely to piss people off!
4 days till the next one....