"Liberal biased" is basically a term used to label anyone or thing that isn't racist, homophobic, Christian, pro-war, uneducated, ignorant, gullible, paranoid, etc.....
The reason those station might cater to the left is because they don't believe the creator of the universe hates gay people so they don't want to support the clowns that think that kids should be taught that earth is only 6000 years old, while also teaching them about the dinosaurs that existed millions of years ago. Talk about breeding ignorance. The war isn't working and it's based on documented lies. What do you except the media to do, ignore it?
The people who make the argument for a "liberal media" are basically saying, "Hey, you're not supposed to tell them that. That was supposed to be secret! Don't be a narc!". Cons are losing because they stand for nothing and they know it. The only way for them to succeed to shelter everyone in society and control the people. That's why Cons rely so much on their AM radio and Fox News. They need something to make them feel good about their ignorance. Liberals don't need to reminded of their concern for the truth. Liberals go to school and let the truth dictate the authority. Cons prefer to have the authority dictate the truth, hence why they only accept information from within. Anything that proves them wrong and contradicts their belief, they label as "liberal biased" and move along. Go figure why so many Cons are religious. It's the same philosophy.
You will never hear Fox News speak poorly of the president because they claims it's anti-American to bad mouth the leader, yet they slammed Clinton for 8 years and continue to do so today. Either their supporters aren't bright enough to see the hypocrisy or they just don't care, because ignorance is the strongest trait in Conservatives.