This website made me reconsider if 99.9999% SLA and always online is really that important for lots of websites. I used to self-host my own server in my own apartment, but gave up on that after my internet provider had their first major outage that lasted almost a week. Also I didn’t want to worry about the fire hazard, or the server going down when I was traveling etc.
But a solar powered server seems interesting, if the batteries could be made fire safe.
That’s the point I’m making: when those examples go down unplanned, in particular hospitals and the power grid, in particular the examples you gave, those can be catastrophic events. I.e., if we ignore planned downtime, then these businesses really need five lines of reliability during the times they are expected to be up.
I agree with the overall point that the average business doesn’t need five nines of availability, but I wanted to point out that there are definitely businesses that do.