I think the problem with the way they do coach comments in general is that what they say is way too influential on the voting results. It sort of offers people a 'comfort in numbers' right at the moment they're trying to make up their mind on whether they liked the performance. So if a person has uncertain negative feelings they are squashed when the coaches are positive and vice versa.
If there was a way to force people to make up their minds before they were influenced by the coach's reaction, that'd be better. But since that's not possible, I'd rather the reaction be vapid and airy, or at least equally ridiculous in the same direction.