I think its more a result of deregulation than anything else. Prior to the passage of the Telecomm Act of '96, there were limits on radio station ownership, both totally and within a particular market, and there was a commitment to local ownership.
Since then, a small number of national telecomm companies now own a larger share of radio stations and programming is packaged, with little local input. Clear Channel, which some would describe as having a conservative bias, went from owning 40 stations in the 90s to over 1,200 stations now, including owning multiple stations in a single market
The bottom line is that radio programming has become homoginized and increasingly difficult to find a station willing or able to take a risk on something new.
An interesting article on radio ownership consolidation:
http://www.stateofthenewsmedia.org/n...?cat=5&media=8