Yup, seems like they have a lot "eventually consistent" batch processing going on. Certain things like CloudTrail have 4-6 hour lags in billing (unless it's improved in the last year)

It'd be a huge engineering effort to make something instantaneous--I think the closest thing they have to such a system is whatever they use for rate limiting or IAM.

I'm guessing there's a pretty high overhead to trying to do realtime instead of batching

AWS oopsies suck but I think their billing system is pretty robust compared to lots of usage based billing systems (like, say, utilities)