This article presents the consequences of the "partisan polarization" phenomenon that we are reading about.

http://www.nytimes.com/2009/02/16/business/media/16williams.html

NPR asked Fox News to not identify analyst Juan Williams as "senior correspondent for NPR" during his appearances on the O'Reilly Factor, because he "tends to speak one way on NPR and another on Fox." Williams made a controversial comment on Fox, which angered his NPR audience.

Knowing an audience expects a certain type of presentation, different news providers (organizations and also individual journalists) will actively cater to "partisan polarization" among viewers.

Ironically, we like to believe that the information we receive is unbiased, but news providers are aware that they are providing for biased viewers and may act accordingly.