Ticketmaster pay a substantial share of their "service fee" to venues and promoters. By signing an exclusivity deal with TM, venues can guarantee themselves a greater share of the effective ticket price. Artists are powerless to negotiate because of TM's dominant position in the ticketing market. It's a grubby little money-go-round scheme that exploits artists and fans alike.

http://www.nytimes.com/2011/06/12/business/12tickets.html