clayj - I'm not really even sure I'm following you; the whole point of a backup is that it exists in two places at once. As a result, it doesn't matter much what medium the backup is on, since if the primary fails you by default go to the secondary. And if you have a very good backup scheme, you have three levels, to hedge against the off chance of a dual failure, a failure during backup, or most likely a failure while restoring due to the same problem that caused the original failure.
Now, I'll freely admit that once an optical disc is burned it's quite a bit less likely to undergo a failure during a restore from backup in comparison to a hard drive, but there such a thing as the price of convienence and the cost of that "fourth nine" or whatever it is. It's just a matter of HOW paranoid you want to be, and what convienence is worth to you. For many of us, it's just not worth going that far.
For example: My current backup scheme consists of a second internal hard drive to which my data is mirrored every evening. I then have a third drive that lives offline in a fire safe that I back up to periodically.
Now, a simple mechanical failure occurrs once every, let's say, 3 years. The chances of even two of those drives undergoing a mechanical failure within one week of each other (the time it would take to get a replacement drive and restore data to it) is extremely small. The chances of all three going at the same time is pretty darned near zero.
Now, a massive computer failure could easily knock out both of my "online" drives, rendering my main backup toast. Which is why I have an offline backup, too--it may be a hard drive, but nothing short of a direct lightning strike to my house (and I don't live in an area prone to that sort of storm, nor is my house the tallest thing in the area) would have any chance of creating an EMP strong enough to toast all three drives simultaneously.
Were I to have optical discs in my safe, then yes, it would be that much safer... but to backup as frequently as I do now, I would be chewing through optical discs at a rate of either 2 a month (for the offline backup) or one to three a day (online). Using RW discs would relieve the cost burden and massive landfill this would generate, but frankly, that's a LOT of time wasted burning discs when an online 2nd drive backup is sufficient for 98% of failures, and 99.9% of the remaining 2% of failures are handled by the offline one.
That said, I ALSO burn DVDRs of finished video projects, just in case. On two different brands of media, in case one develops bitrot, the other will hopefully not have rotted as fast.
