in one case, anyway, and the reason is because QTrax, the operators of the service, are paying most of the revenue they receive from advertising back to the rights holders. The music companies will have a revenue stream, and so will independent rights holders, once they've been identified by QTrax - who will pocket the remainder.
The scheme will work if QTrax can attract enough advertisers, and they should be able to do that without any difficulty. A service that permits consumers to download music legally, with the full support and cooperation of the copyright holders should do very well indeed.
At last the industry is taking a step - albeit a tentative one - in the right direction.