As concerns the success or failure of political media, I was addressing what you seemed to be implying, and I called you on it. But if you weren't implying that, I'll let it go.
To more directly address the question in the OP, did you try Googling around a bit? From
the Denver Post:
The consolidation of ownership of radio stations is at least partly responsible for the statistical dominance of conservative political talk radio.
"Toxic Talk" by Bill Press, is a prickly takedown of the "destructive power of Rush, Beck, Sean Hannity, Michael Savage, O'Reilly and the other polarizing figures of talk radio." The book's subtitle says it all: "How the Radical Right Has Poisoned America's Airwaves."
According to Press, "the key is ownership. Follow the money." In the case of Clear Channel, he notes, the company owns 145 news-talk stations and also owns Premiere, the top syndicator of conservative talk shows, which syndicates "The Rush Limbaugh Show," "The Sean Hannity Show," and others. Clear Channel, in turn, is owned by (Mitt Romney's former venture) Bain Capital.
The biggest U.S. radio station owners — Clear Channel, Entercomm, Cumulus, Salem, Cox and CBS — establish their 50,000-watt blowtorches, like KOA in Denver, as the home of conservative talk. "And you wonder why it's so hard for a liberal to make it as a talk radio host?" Press writes.
Talkers' Harrison argues that anyone who wins ratings, regardless of viewpoint, would be welcomed by a financially driven corporation. It's about drawing audiences, regardless of ideology. That's been the Clear Channel stance for years. Press disagrees. A liberal talk radio icon is an impossibility, he suggests, due to the corporate ownership of the media.
There are more Dems than Republicans...and while more identify as "conservative" than as "liberal", when it comes to the social aspect of the ideologies, we're now split evenly...and the momentum clearly shows that social conservatives are diminishing over time as social liberals are increasing over time. All of which means that there's no reason why liberal talk radio can't compete when it comes to raw numbers of listeners. That's why the above reference is so important - there's more to the story than just the number of listeners.
But there's a silver lining for us liberals - I think it's safe to say that while conservatives still have a choke-hold on talk radio, we liberals are much more successful when it comes to talk shows on television. Oh, I know, y'all have Bill O'Reilly...but I'm referring more to the daytime talk shows and the late night talk shows that do lean significantly to the left. Yeah, they all claim to be politically neutral...but it doesn't take a genius to see where their political hearts are. They just have to maintain a razor-thin veneer of non-partisanship.
So...y'all go ahead and keep the radio waves - we've got the non-Fox television giants. See y'all in November!