Wumpus, thanks for the clarification. I think the [de]evolution of rock radio can be summed up thus [but if anyone believes otherwise, please chime in]:
60’s: AM major market: Top 40 defined and payola-corrupted, but not limited by genre or race.
nascent FM markets: DJs get to “go commando,” with virtually no corporate strictures. The FM freeform rock radio golden age.
70’s: AM declines due to the no static at all* appeal of FM. [thanks, Steely Dan!]
FM stations adopt rigid, albeit station-determined, formats (like “morning zoo” blocks) and station programmers draw up [payola-influenced] playlists. But I suspect that most FM DJs still managed to enjoy a degree of personal autonomy.
80’s: AM stations mostly converted to news/talk/religious/etc. formats.
FM stations increasingly bought up by larger broadcasting/media companies, up to the limits defined by tight federal regulations governing corporate ownership and concentration. I believe that playlist control, even in the late-'80’s, was still mostly locally determined; i.e., drawn up by the station programmer (who, more often than not, was himself a former DJ at that station, promoted to that executive/managerial position).
90’s: Federal deregulation of the broadcasting and media industries. A wave of corporate concentration ensues, with the result that almost every FM station is owned by one of five giant media conglomerates. Clear Channel in particular innovates money-saving and market-homogenizing practices, including the culling of DJ staffs and using a few DJs to host programs broadcast by multiple stations, and the supplanting of station-level programmers by central office marketers, whose music picks are then imposed (by genre) on all the corporation-owned stations.
One example will suffice: or, how I became a Flaming Lips fan. About three, 3 1/2 years ago, I heard a DJ play a wonderful song I’d never heard before. Luckily, she identified the artist and title (“Buggin’”) immediately after playing it, before going to commercials. I immediately bought The Soft Bulletin, and exposed my friends to it, and bought another copy for my brother. I only heard “Buggin’” on that station that one time. Not long after that day, the family that owned that 'Jersey shore station, which had been an independently-owned holdout, turning down one buyout offer after another, sold it to one of those big companies. Although I still tune in occasionally, it’s just a format-check on my part, to hear what’s playing. I can’t bear to really listen for more than a few minutes. It’s all like a real-life version of Invasion of the Body Snatchers!
The overall situation is just so depressing. I think of people like my aging parents, who think that most new music is crap, which is probably a natural enough response anyway, but is almost justified by their very shallow exposure to what’s out there, which isn’t much. 