Per-site reliability (beyond a stated/assumed 95%, which is right around the "I put a computer on my desk" level) isn't a design goal, though. You can argue with their math or their assumptions, but you can't say they're wrong for not designing in the reliability features you list above.
I think it very much depends on the desk. I mean, power alone at my home just barely reaches three nines. Internet connectivity glitches out occasionally. I'll fat finger configurations and reinstall stuff for some more hours a year. It all adds up.
You're right that you can take the same hardware, add a $70 UPS and some thought and care, and do much, much better. But my point was only that "95%" is a trivially achievable goal even in the most naive setups, which makes me treat their analysis with a little more credence than most folks here.
