This is an important and great question. There are a number of ways in which watching something and listening to something is different. Let me give you are few of these very important differences.
First, when you are watching something, you are using many senses all at one. You are seeing something and listening to something. In fact, if the volume is loud, you might be even feeling something, such as a deep base. So, we can say that there is a sensory overload. Hence, the person trying to communicate something to you has more to work with. The only downside is that the presentation usually must be done in one sitting. Therefore, the person must be very selective.
Second, when you are reading something. Often times there is only two senses in an ordinary format. You see written words and if you read out loud or someone reads to you, you hear the words. In other words, there are limitations. However, the upside to this is that reading can be prolonged. Therefore, uou are able to communicate in time. There can be more development.
In continuation to post one, with which I agree, there is another major factor related to visual media. At present TV (Visual Media) is able to create a hype by repetition and can influence the audience more effectively as many sensory organs are responding to the audio-visual format.
In written media it is difficult to create a hype with a comparable intensity of the visual.