Rush Limbaugh hit it big originally because he tapped into one of the Great Liberal Secrets of Success. He learned that while it was once advantageous to feign strength and power, it is currently (since the 70s in America, if not before) more advantageous to feign weakness and disadvantage.
When dealing with any large group of more or less moral people, you no longer want to be perceived as being a bully. You want to be the one who's being bullied, because that way you have people's sympathy and support instead of feat and hatred.
Every civil rights movement utilized this kind of tactic; they emphasized how badly they were being picked on by those in power, and consequently gained public support.
Everybody, especially in America, like to root for the underdog.
The difference being that the people in civil rights movements actually WERE the underdog, but the new form of Republicans spawned by Reagan's era were the over-dogs.
It's hard to feign nobility or justice when you're the one in power, but Rush apparently realized that this was the only way to win.
So he latched onto another of the Great Liberal Secret: "Everything is relative."
This secret was utilized by hippies and beatniks in order to rebel against the established order, against "The System."
They started questioning everything around them, and they reveled in the power.
They questioned authority, and it paid off for them, at least in the short term.
Rush used the whole "everything is relative, who are you to judge me, question autority" gimmick against the people who (at least in modern America) more or less invented it.
So he started churning out memes:
"It's not that MY show is biased towards conservatives, it's that the rest of the shows are against us! The Media is Liberal!"
"Welfare moms are bankrupting the country!"
"Liberals hate America!"
"White people, especially men, are a persecuted minority!"
"It is better to be corrupt than to be lazy!"
And a bunch of other crap that nobody in their right mind would buy into, except for those two stolen Liberal Secrets.
By playing at being the underdog, Rush gave neo-conservatives a get-out-of-guilt FREE card for their crappy behavior and agendas. They could do what they wanted, say what they wanted, and anybody who disagreed with them could be dismissed by claiming that the person must be an oppressor out to stifle the poor, perfectly-reasonable neo-cons.
Or they could be dismissed by Questioning Authority.
Sure, they might have a PhD in the subject, but who are they to say what is right or wrong?
So now we have FOX News, which is a couple evolutionary steps down from Rush. It uses his discoveries to great effect, spreading conservative propaganda while claiming that they're the only ones who aren't biased.
"The poor oil companies are just trying to make an honest living, but the whole global warming scam was invented by Green Power companies trying to con people and the government out of their hard-earned cash."
"Christians are always loving and peaceful people, but they're persecuted everywhere by haters (even though America is rightfully a Christian nation!)"
In short, they're doing what any other hate-group does, prey upon people's greed, hate, and paranoia, and stirring people up against each other.
They're not only a bad news network, since bias is what pays their bills, they're simply BAD for the country as a whole. They stir Americans up against other Americans, to the point of hating each other, in order to line the pockets of an Australian (and, of course, themselves).