I don't know how cloud services count usage, but this is certainly not true for telco. I manage several fleets of hundreds/thousands of SIM cards (mostly IoT/M2M applications), and almost every provider counts the data traffic per byte. Different business and use case, I know, but still.

The way you describe requires somehow counting every bit but somehow discarding most which is obviously nonsense.

This seems statistically invalid insofar as it will tend to overbill potentially by a lot on the minority of cases.

Don't you know how much of the pipe is occupied by a given customers code at any given time or what data is being sent