Exactly. Also it's different when you are talking to one person vs 1000s of people. Even when it is obvious, 0.1% of readers will read it just a little to quickly and get confused. Given that "/s" makes it more obvious, the intentional omission of it is intentionally requiring more effort of the readers.

There are times and places when one might want to make the readers work harder, but HN comments doesn't seem to qualify.