No its not payola, its positioning. Radio as in any business has inventory and that inventory is the time slots on air. When radio gives up 3 minutes to an artist they basically are giving away 3 minutes of that inventory (that you can't replace. You can't replace time) So the labels take (for the lack of a better word) their place in the line of records to be added by backing station endorsements and contest (which is a plausible business practice). The more you spend or support the stations efforts, the further up that cut line you can be (ie you support me, I support you...). licensing groups made it worse by trying to overcharge the stations with licensing fees so the stations started charging to get on the cut list because they felt they were being overcharged (extorted) by BMI, sesac and ascap for airplay licensing fees (in reality the licensing groups created this animal and the artist and the labels were handed the tab. (Licensing groups are like girlfriends who know everything except how to put anything on the tab.)
In reality most artist would do better by just buying ads on air in a serious ad campaign like any other business, but if they did that a lot of the middleman culprit power brokers in the music business would be out of business. Buy you an ad campaign like any other business and if your product is truly market worthy, it will stand on its on. You aint gotta sell good dope, good dope sells it self