Lawrence Lessig has an excellent report from Australia on the course of media deregulation and consolidation in the land down under the thumb of Rupert Murdoch. The key paragraph describes the tipping point beyond which resistance is futile:
Once media concentration is allowed to creep past a certain point you are in trouble. The media owners can push for more concentration due to the fact that they control public opinion via TV and print media.
Australia is a very different environment in many ways, and probably calls for a solutions to media concentration. But most of what has happened there is basic economics and politics.