Our dojo has no hard and fast rules on talking, obviously standing around chatting instead of training is frowned upon... but talking is accepted. Generally if you are the higher grade of the two practicing and the other is making an obvious mistake in technique then some people will correct them.
When I teach a classes I quite like to see begginers explaining things verbally to each other. Teaching is one of the best ways of learning something or getting it set in your mind as you have to break it into small understandable chunks and internalise it yourself.
I still can't see why it would be necissary to train in silence. I may try it with my class some time.. I think it would be interesting to watch them communicate without words.
Another reason I like to allow people conversation is because I often use it to distract people in the middle of technique. Not to make them do it wrong, but instead because they are over analysing and when I can get them to do it whilst thinking of something else they tend to do it spot on.