You can never really be sure whether you have somebody's full attention when you are typing to them. Since that person is not sitting in front of you nodding, looking at you, falling asleep, etc., you can't be sure that what you are saying is getting through to them, either physically getting the words across the network, or if the words do get through, whether that person is watching your words. In fact, that person could be out of the room, asleep, in the bathroom, or out of the house. There is a certain amount of trust that has to be put in place to ensure that your audience really does care what you have to say and will stay put while you are talking.