A quick look at radio pre-1996 when the Telecommunications Act was passed by Congress.
Radio stations were largely owned by small business owners, mid-size companies and a few large media corporations. There was a diversity of programming and many of these broadcasters were in the business because A) they wanted to make money and B) they knew and loved broadcasting. (Obviously this is a generalization, but it's basically true.)
After 1996, big corporations had the authority to buy up more and more radio and TV stations, thus setting up market near-monopolies. To pay for these acquisitions, smaller broadcasters merged with each other to form mid-size companies, or sold their properties outright. A few major corporations merged and became the behemoths we now see. This was all funded by debt and required these huge companies to cut costs -- cuts that have deepened this month due to the overall Wall Street meltdown.
The biggest change to the business is that today you have hundreds of stations that are largely or fully automated or voice-tracked, and I dare say that a burgeoning majority of stations are voice-tracking overnights and weekend. Pretty soon, there will only be a relative handlful of air personalities in any given market. And new talent will not be developed.
Listeners, who are not stupid (depsite what the average Local Sales manage usually thinks), have noticed many of these changes and are voting with their choice of listening to music on IPod or perhaps satellite.
Corporate radio is concerned with one thing only, financing the debt, and, in the case of public companies, fulfilling shareholder obligations. The days of a great local broadcaster being a businessman or woman who ran a couple of stations for fun and a small profit (or, heck, a tax shelter) are mostly gone.