What makes country, country?

What makes country music country? Matt and I argue about this all the time.... Is it how the singer looks? Is it the lyrics and what they sing about? Is it the sound and the instruments? And what if they only have a few of those qualities and not all of them? Does it cancel it?
Matt's consistent example is the Eli Young Band. Their style of clothes & hair: rocker/hipster-ish. Their lyrics: country. Their sound: unique... a hybrid. He claims that this qualifies as not country. So what is the deciding factor? If we look back to Merle Haggard, Conway Twitty, Tammy Wynnette, Johnny Cash..... their music and their style is totally different from what we qualify as country today. But is it simply the time? Is it simply the evolving of a product, the same as a dial-up Internet evolving into DSL... or the teal colored refrigerators being replaced by stainless steel ones with TVs on the front.... So is there room for the growth of a genre? Or is it consistent through time? With everything that changes, there's people who love it and people who hate it. Our grandparents may think having our cellphones glued to us is annoying...but we may see it as efficient. Facebook may seem as unnecessary by our parents... but our generation sees it as an effective way to communicate and connect. There can also be a mutual respect for the past as well as the changes of the future. There's nothing wrong with Hank Williams Jr. and there's nothing wrong with Tim McGraw.... it's just different. I think placing an artist into a genre will continue to be a relative, opinion-based decision.... but it's interesting to think about. Trends always seem to come in cycles too....so does that mean in the next 10 years we'll see the next Johnny Cash or next Tammy Wynette come back onto the scene? Stay tuned!