EC2 used to terminate instances with no warning in many situations when it launched. It seems they've concluded most people didn't understand that, and avoid that whenever possible now.

But "cloud" compute services should in general be treated as less reliable per individual unit unless your provider explicitly explain to you why not (such as guaranteeing to use a high-availability distributed filesystem), as you no direct way of ascertaining status of the underlying hardware. You need to plan for failure regardless.