You're (probably) not wrong about the abuse thing, but it sure is nice to just not care about that when you have fixed hardware. I find trying to guess which of the 200 aws services is the cheapest kinda stressful.
We're hoping to write a case study down the road that will give more detail. But the short version is that not all parts of the client's organisation have aligned skills/incentives. So sometimes code is deployed that makes, shall we say, 'atypical use' of the resources available.
In those cases, it is great to a) not get a shocking bill, and b) be able to somewhat support this atypical use until it can be remedied.
Why would it be abuse? Serving e.g. map tiles on a busy site can get up to tens of thousands of qps, I'd have thought serving that from S3 would have made sense if it weren't so expensive.