This comment over in the Ars forums:

The need for backups was more of an issue back in the days of magnetic media, where the originals could and did degrade over time to the point of being useless.

reminded me of this comment by Jack Valenti, former president of the MPAA:

Where did this backup copy thing come from? A digital thing lasts forever.

A while ago I bought GoldenEye on DVD. New discs of this Bond movie are not being made anymore so I bought it used. The disc did not have any noticable scratches yet all my DVD players were unable to play the last 30 minutes of the movie. Most likely a bad case of DVD rot.

Jack, DVDs do not last forever, but comments such as this one probably will:

I say to you that the VCR is to the American film producer and the American public as the Boston strangler is to the woman home alone. – Jack Valenti, “Home Recording of Copyrighted Works,” Committee on the Judiciary, United States House of Representatives, April 12, 1982