Marketing surely takes advantage of it, but I think this has more to do with the addictive, yet passive nature of TV, where we let it push images into our brains.

My favorite example (for which I've already given away the punchline) is the following:

Ask a random group of people to imagine that they are watching a baseball game. Give them a minute to think about it. Then ask them -- Are you in the stadium? Or watching it on TV? The amount of people who visualize TV as their first reaction can be frightening.