I think the traditional news outlets (NY Times, the big three networks, etc.) have moved to the left.

In turn, that leftward migration allowed the rise of non-traditional outlets for conservative opinion (e.g., talk radio, the internet).

However, as noted ad nauseaum in this thread and elsewhere, the media itself seems to label only one side of that dichotomy. Conservatives are labeled "Right Wing" and sent to the talk radio/cable TV ghetto, while liberals are allowed to wear the mantle of "mainstream" or "objective" and allowed to host the network news.