Interesting, I saved roughly 2M USD / year for customers moving them to the cloud. Your example is silly, all of the CDN I set up has very strict limit on how much a single IP can use and have multiple alerts if you are passing 100, 200, 500, etc. USD limits. On the top of that if that is not enough you can add more limitations to avoid that exact scenario that a public resource can be abused to cause you financial troubles. It won't "bankrupt" you if you do it right. Just like pretty much every other technology, you need to know it.

The other problem with your comment is that you try to make it sound like it was a single dimension decision to use the cloud. It is never a single dimension questions though.