Artist Vs. Song

I recently asked for blog post suggestions on Facebook, and Kyle Gardner suggested a very interesting topic. Here is what he said:
"My Dad always said in his day songs were popular not artists. Artists would remake the same song. I always thought it would be interesting to research this. I like the idea that the music is the star not simply the musician."

I like this. This has always been an interesting concept to me. Why is it that these days everyone knows about Britney Spears, but only a handful of people know more than 10 songs she has released? On the flip side, why does everyone know the song "Twinkle Twinkle Little Star" but few people know who wrote it?
Obviously those are just general examples, but there is a point behind it.
These days, money is poured into people or acts with the proper image, top notch performance ability, and talent. Many writers may go into composing one Justin Bieber song.
Back in the day, things were different. One person would write great music, and perform it brilliantly. These people caught the attention of record labels, who might offer some extra income by selling recorded music.
Written music was extremely flexible. Take, for example, "Ain't No Grave" If you're thinking Johnny Cash, then yeah, that song. But that's a pretty modern way of thinking.

You see, "Ain't No Grave" was written by a 12 year old boy named Claude Ely in 1934. He was sick and bedridden, so he taught himself how to play the guitar. When he was told that he would be dying soon, he said "No I most certainly am not" and played what would become known as "Ain't No Grave." He got better, attributed his health to an act of God, and went on to become a travelling preacher playing that song frequently.
This song has been released dozens of times by dozens of chart-topping bands and artists from a wide array of genres.

So why is it that once a song is released these days, no one is allowed to touch it? Why should that be ruled off limits for promotional purposes? Why do we let the artists become the stars rather than the music?