When liberals accuse the media of a conservative bias, they say so for one of two reasons. The first is a lame attempt to defeat a harmful fact by simply contradicting it with the opposite of the truth, a kindergarden-like accusation ("You hit me! No! You hit me!).
The second reason is the view that the media, as instruments of the free market, are "conservative" because they are not socialist institutions, like The People's Daily of North Korea. The profit-seeking media condemning profit-seeking is one of those bizarre disconnects conservatives have learned about liberalism. And again, it is the essence of liberalism: the inability to relate principles, personal behavior, and political views.
I remember with utter clarity, how William F Buckley -- the lonely public voice of conservatism in the 60's -- was regarded by liberals as a nut case and extremist. Any human being ought to have been able to see that Buckley was a gracious, gentle, principled, courageous man of remarkable equanimity. But liberals could not see that, so essential was their childish confusion between their politics and their principles.
Radio is personal and intimate. Radio does not tolerate phoniness and absurd artifice, as so many of the other media do. (Limbaugh and Stern ... strange bedfellows, but cultural twins.) Liberalism does not need an attitude adjustment ... it needs an attitudectomy ... but then it would not be liberalism.