Scaling to exabytes and beyond

I know dropbox isn't the only company to publish numbers like this, but it really bugs me. This is 12 nines, or 1 in 10-trillion.

To put this into perspective, the earth is 4.5 billion years old. During that time, we've seen multiple mass-extinction events. Suggesting that there's a less than 1/1e13 chance of cataclysmic event (megavolcano, nuclear war, pandemic) next year, when there have been many in the past 4.5e9 years, is ridiculous.

But, I hear you say, maybe they're talking about only a certain class of issues -- failures in their stack itself. First, I'd say that they should make that clear. But second, surely the chance that there's a bug somewhere in their stack (going all the way from their datacenter silicon to internet infrastructure, to consumer machines, and back) is greater than the chance of e.g. a cataclysm sometime in the next million years.