Radio airplay is a crucial element in getting your music out to the masses but not all airplay is the same. Major radio stations in each market reach the most people and are the go to's for each city.
However, getting airplay on the major radio stations is very hard because there are so many records and artist and only so many slots available.
It is also crucial to understand that major radio station are in the business of playing "hits" and not to "break" records. Radio station only play what the masses want and what is popular overall it is still a business with a lot of money tied to it.