Exactly. Which is why the AC/DC guy did it manually, that along with the previous commenter's point of not wanting to have an unused "open" mic gained up when between vocal lines. This was probably more the case with AC/DC since there wasn't much baritone in that set.
I have a strong suspicion that the new Gnr FOH guy is not riding it manually and that's precisely what's causing the somewhat sloppy sounding extreme peaks and valleys in vocal signal this tour.