I talked to the old CEO of TicketMaster years ago about the fees and when I found out that most of the service fees are kicked back to the venues, I found them far less evil. They take all the blame that should be directed at venue owners.
1) Venue relationships 2) Taking the fall on fees 3) Ability to scale
People are often surprised by #3. Having seen many startups try & fail (as well as large entities like LiveNation), ticketing is a hard problem.
In my time at Yahoo & Google, I believe they have the technology to build a ticketing company, but beyond on that, most -- startups to large entities such as LiveNation & CTS -- had big problems handling onsales for large U2-sized events. In fact, it always made me think "Good luck with that" when people would talk about the design of ticketing systems using relational DBs. :)
They could combine their fees into the ticket price, but they're afraid the artist will also demand 90% of the combined ticket price, putting significant risk on the table for them. Their motivation is minimal: People still buy tickets & nobody ever blames the venue or promoter. So from their viewpoint, why change?