Therein lies your problem, I think the key is to rely on the data itself, not the mediums. As you say, DVDs and CDs are not permanent, but the data can be.
These days there are many off-site back up solutions, like Amazon S3, Google, Dropbox, Box.net etc. In the event that the internet goes away overnight, and all these companies go bust without warning, then you may have to rely on your hard disks/DVDs. However, it's far more likely we'll lose our negatives in floods/fires/theft/accident etc.
Don't get me wrong, I'm a film guy, and I'll argue for film all day, but for backups, digital has it film beat easily.
In your examples, there is nothing wrong with the technology, just the way it's used. If used correctly, digital files will outlast us all. The problem is that most of us don't use it correctly.
Much as I'd like film to be better for backup, it just isn't.
But you're right of course that digital backup is just as susceptible to mistakes as a box of negatives. However it is so much easier with digital to prevent the mistakes in the first place.
Cheers
Garry
It is no myth that CD's & DVD's are less than permanent media. I'm already experiencing loss of files on CD's burned several years ago.
The newspaper from which I retired cannot access photo files stored on early digital media due to failures of media readers and/or obsoleted operating systems that supported drivers not supported on current computers (Power PC v Inten Macs). Personnel cutbacks resulted in a loss of oversight of the photo archive that might have seen this issue evolving and transferred the files to current and more stable media.
They since have gone to a mish mash of outboard HD's (likely not as cohesive as a RAID array) which introduces other issues such as cataloging.
Not much different really than storing negs in paper envelopes in hot and humid attics and wondering why they eventually go to ruin.