I would almost argue that music of their time was even more disposable, just in a different way. The common artists had no way to record, and usually didn't have the education to write it down. So music lived and thrived in a live setting, but could then be forgotten. As much as I love music and the physical medium, something about that just seems so special. Every performance is different and original, and definitely improvised upon. It's been awhile since my music theory and music history classes, but we had an extensive portion on secular music during medieval and renassaince times, and it was so different; the sound was really more comparable to Bluegrass or squaredancing.

Although, I dunno, I'm iffy on big picture questions about art, like this. It's fun to discuss and analyze, but I'm also afraid it will color people's opinions more than it should. In the end, it doesn't matter if an artist is a trailblazer or totally disposable, if it's entertaining or it speaks to you, it's important. I don't mind my CD case having Chopin's complete works sit next to Katy Perry's Prism. They both have their own place and importance, and I wouldn't give up either.

EDIT: To clarify, I think beyond analyzing certain trends, art is much better discussed on an individual basis. I don't like terms like "disposable" because they can so easily invalidate the opinion of someone whom that song deeply touched, silly as it may seem.