Somebody explain to me the whole Johnny Cash thing

The latest round of the Rolling Stone 192 Tournament is up, and two Johnny Cash songs are poised to make the round of 16, with only John Lennon and Stevie Wonder standing in front of them. I don't really get it. I'll grant that when you're narrowed down to a field of 16 songs, it's not entirely unfair for the Beatles to only have one entry (especially since they're not nearly as popular with some voters as they are with me). But what is up with Johnny Cash that there is a strong possibility he'll have more songs in the final 16 than will the Beatles?

I've listened to the songs in question, "I Walk the Line" and "Ring of Fire." They're fine, I guess. "Ring of Fire" is catchy enough. But why are these songs so great? The music is pedestrian, the lyrics acceptable but fairly simple; Cash's voice is interesting but doesn't evoke much in me. And on top of all that, the two songs just sound pretty similar to me.

Certainly people are entitled to their opinions on Cash, and I can respect that, just like I can respect (although massively disagree with) people who think that the relative trifle "California Girls" is better than George Harrison's masterpiece "While My Guitar Gently Weeps," and such. (Though I cannot respect the opinion that "Strawberry Fields Forever" is a bad Beatles song.) But I'm wondering if it's possible for his allure to be explained at all, especially against some of the best songs in rock history. ("Line" and "Fire" have combined to defeat "Fortunate Son," "Bohemian Rhapsody," "Both Sides Now," "Waterloo Sunset," and "In My Life;" I consider only one of those five songs not to be better than both of Cash's put together, but again, that's me.)