Artists that use the same song structure...

Czarivey, you are wrong about bluegrass. I've taught and played enough of those songs to know that it's not so one-dimensional. There are subtleties and musical variations that you apparently have not yet encountered--I know it's not a matter of them "going over your head." For instance, there's a lot of different melodic modes and different chord progressions. You will hear some of the same ones repeated, and often, but there's a lot more there than what you've mentioned.

Phasecorrect, I agree--good is good and bad is bad, regardless of whether it's primitive, complicated or somewhere in between. Of course, it's subjective and there are no absolutes in this matter.

Czarivey, trust me, it takes genuine talent to play bluegrass well. I don't care for most of the modern examples of it but I respect the musicianship.
You can also sing Folsom Prison over the changes to Pinball Wizard, and vice versa, but that doesn't diminish the value of either song IMO.
Not a fan of Phillip Glass, but at least he's repeating himself intentionally to achieve a certain effect.
Anyway on the bluegrass the new vocal people mostly don't ring my bell (I like Tim O'Brien) but the instrumentalists such as Sam Bush, Tony Rice and Jerry Douglass are phenomenal musicians. It takes real skill to do what they do. Try it some time.