This article in today's issue points to the lack of new adds at radio stations as a direct result of New York Attorney General Eliot Spitzer's anti-payola campaign. Simply put, music and program directors are less inclined to add anything other than established hits for fear that it will draw attention to the stations and put them at risk for investigation. Maybe I'm cynical, but it didn't seem like radio stations were reaching far outside of the box before payola reared its head again.
If you're interested in the historical background of payola, I suggest Payola in the Music Industry: A History 1880-1991 (Segrave, 1994). This seems to be the most compresive work on the subject and is cited frequently in academic texts involving media ownership and, specifically, the music industry. Don't let that turn you off, though, as it's actually an enjoyable read. What this book essentially does is put payola into context. Like everything else, it appears in cycles and payola's presence generally ushers in a new era for the radio industry. However, we aren't talking about open playlists, as Segrave ties the stagnant AM playlists of the 1960s (which gave rise to FM rock radio) to the payola scandals of the 1950s and early-1960s.