Of course, the vast majority of the radio stations are now actually owned by the same evil multinational conglomerates that own the four record labels that actually get sales.
Case in point - Mariah Carey signs to Sony, marries Tommy Mottola - head of Sony in the US. Mariah Carey records get played on radio stations owned by Sony. A lot. Mariah Carey divorces Tommy Mottola - suddenly her records get a lot less airplay.
The fact is that payola is no longer necessary, simply because the radio stations and the record companies are the same people - which is why (at least in the US - in the UK the most listened-to stations are non-commercial, so slightly different rules apply) no good new music at all makes it on to the radio.
Of course Mp3.com have brought payola back for the 21st century...