I disagree.

Music can never be devoid of originality. You will always find new production techniques and new sounds that will sound totally unlike anything before. For every cover or a song that uses samples from older songs, there are a hundred other songs that are totally original and unique. The only reason I find you came to that conclusion is because a lot of mainstream and commercial (which 95% of is mindless dribble anyway) rehashes older songs to appeal to a wider audience.

However, delve a bit further and you'll see bands and singers that write their own music, which make their songs totally unique. I can several just off the top of my head: Bloc Party, Franz Ferdinand, Outkast, Martha Wainwright, Scissor Sisters, Wilco, Wolfmother - and the list goes on.