You raise an important concern, but I wonder if the analogy is the right one. For a lot of startups/businesses, a period of downtime (in hours, not days) is not death. It might suck, but you won't die. In the late '90s, Ebay was down for three days straight (!) and it's still doing OK.

I will be surprised if Amazon doesn't work out the reliability issues anyway, given the massive resources and smart people it has available to it.