Obvioulsy backing up any type of art or data is never foolproof. Analog masters could be destroyed by fires, etc., or I suppose the tape itself could just age and fade. I've personally never had that problems. I still have four-track cassette tapes that I recorded when I first started in the mid-eighties, and the music on them still sounds just as shitty as when I first recorded it.

And that's with no thought given to storage whatsoever. I imagine that analog masters of important albums are in pretty good hands.
I don't think anyone is suggesting that analog masters will last forever. It does make sense to me though that it's a more robust storage medium in that it's simply harder to do damage to the whole thing (unless you do something like store it next to your magnet collection or something). I mean, you could jump up and down on a cassette tape and smash the casing to bits or slice and dice a R2R tape to bits and still probably be able to retrieve just about everything on those tapes, whereas if you did the same thing to a CD or hard drive, you'd be SOL. (Obviously magnets are the achilles' heel of analog.)
I dunno ... I don't mean to get on a big digital bashing session. I think it's awesome for certain things. I just don't prefer it when it comes to music.