I must say there's some nice writing in this thread, and I'm quite enjoying it.

Back to the core subject though, it just occurred to me that "covers" is all there was before we had recordings and radio. I've got a collection of Etude magazines from the first few 1900s. I'm sure many people here are familiar with those. You'd get the magazine, gather around the piano with mom (who could read music) and that was the radio. It's quite obvious that there was no other way to get the original composer/performer into your country, back woods town, or living room.