Disks fail, especially since most of them still floating around are 20+ years old.
Call me crazy, but I like for my backup solutions to be more reliable than that.
guess you didn't see jest in my post eh;)...btw what you say 'may' be true for long term backups but when transferring from one HD to another the results are immediate if you encounter a 'bad' disk and I've still got lost and lots of disks to spare lol
btw, IMHO I still have C64 5.25 floppies that work just fine today and yes I've got them backed up to d64 files nowadays but the information is still safe on them today...don't get me going with that crap CD/DVD bs