It is more common than not where my daughter competes, for the judges to turn away during warm-ups. Often they will turn to watch another event competing or just turn their chairs around and chat with each other.
I have worked timing at 4 different meets, and many different levels and events at those meets... Bars, Vault, Floor, Beam... Levels 4, 6, 7, 8, 9 & 10 (yes we had to work a LOT at the meets hosted by my daughter's old gym) and I have never even seen judges pay attention to the warm-up at all.
Maybe this varies by location though... Who knows.
I can agree though that the commentary from the judges sure is interesting. And it definitely doesn't always involve the skills the athlete is doing.