I guess above.net hosts them to increase their peering muscle. Presumably they have arrangements with other huge ISPs whereby whoever sends the most content (bytes) gets paid for the difference... so the more they send, the more they make (or the less they have to pay)
It's been a few years since I looked into that system so it may have changed now.
Gasper: there are no ads at all. I've listened to it heaps the past few days and I've heard about 4 voiceovers in that time. Each one was a station and/or DJ identification.