I would agree with this. Silent treatment, in person, is probably one of the worst punishments I can think of. Even when my boyfriend is distracted, there is nothing worse to me than feeling ignored.
I would think even in person this punishment could still feel like an abandonment, at least for me. I could see it as being used as a last resort punishment, though I suppose it depends on the effect it has the sub. For me, it would be devastating, but for someone else, it might not be as harsh of a punishment.