That threat even has its own name now: a denial-of-wallet attack.

The limited protections available against this threat from the big cloud providers have to be seen as a warning sign. It's only a matter of time before any small business using these services for hosting can be subject to sudden shakedowns by criminals. "Nice business-critical infrastructure you have there, be a shame if anything were to happen to it." Some of the providers do offer a DoS mitigation service, but the cost for the higher levels can start to look like a shakedown itself.