By that logic a write to a postgres table would also count as N+1 writes, where N is the number of secondary indexes defined on that table?

And also, by the same logic, replicating a write to three machines counts as three writes when the replication factor is user-defined, right?

For purposes of this benchmark, the first yes, the second no. But neither of them are free.

Well fair enough but that method of counting is not what everyone else does or assumes, so somebody just reading the title "120k writes per second" gets the wrong impression of whats going on.

(An uninitiated reader would assume you're comitting 120k rows per second from the title, whereas it's "only" 12k rows and "only" 3k actual operations over the wire. Still, 3-12k is pretty impressive)