yes that is small, and an interesting hassle I hadn't thought about. I would think you could have the option to set a cap so that it stops using services when you hit it, but they don't allow that. A labyrinthine pricing model, coupled with the forced hookup to the credit card for the free tier (that apparently they'll keep trying to charge against and come after you for if the card is cancelled, or you try to self-cap by only having a certain amount on the card), makes for a big distraction, afaic. It is a hypothetically essentially infinite potential suck of your $$... that you will be at the mercy of Amazon customer service to resolve. Now, this has not apparently happened (or I assume we would have heard about it), but the mechanism is in place. Maybe it's just usually a few hundred dollars - curious how often it happens.
I must be about the only one to be concerned about it. Lots of folks obviously seriously rely on the services aws provides, and do not lose sleep over the possibilities here given the benefits they enjoy from it.