[suresk]

Having a "hot spare" cloud provider is going to be so complex and expensive that it probably would kill the idea of using Azure, Amazon, etc for most companies.

Unless you run your own DC, you are still outsourcing part of your infrastructure to a colo facility, which will not be immune to power and connectivity issues, and of course, issues with your setup.

Saying "<cloud provider> is down" certainly isn't very comforting, but if the aggregate downtime is less than if you were running your own setup, I'm not sure that being powerless in the event of downtime is reason enough to not use them.