Guys, the thing you have to remember is that radio is like retail. If a product doesn't move, it's replaced with something different, with the hopes that it will move. Radio stations will flip formats. If one format doesn't grab listeners, it's replaced with something else.
An interesting note is that one format might work in Chicago, but the same format won't work in Los Angeles. Each demographic is an experiment in itself. You keep trying things, keeping the stuff that works, and discarding the stuff that doesn't.
The same goes for radio personalities. In some areas, one personality may be what the doctor ordered; however, if that person moves to Phoenix, they may come off like a thorn in the side.
One other problem today is the proliferation of other programming sources, such as iPods, web streaming, cable and a lot more. Broadcasters have to work really hard to get people away from their iPods and get them to listen to their station.
Unfortunately, if a station you like flips formats, it means that a lot of people didn't like it; so, station managers/programmers have to try something new. If you like what's new, good; however, the station is going to try things until everybody listens to what they have.