I think that's exactly the difference. With in-class grade reporting, you know it's coming inside a 6-7 hour block of time. Even more precise if the assignment was for a given class. With real-time grading, you could receive the grades at the breakfast table on a Saturday morning.

And the real-time grading is likely tied into how unhealthy other online forums can be. The student could get in the habit of just waiting for the grade (refresh, refresh, refresh if it's a web page).

I finished high school before there was any automatic grade reporting (for assignments). And report cards were sent on a known schedule (and received a day or two later in the post). It wasn't stress free, but at least you could mentally prepare for the bad news.