I wouldn't be surprised if all Ticketmaster customers are unknowingly agreeing to arbitration and waiving their right to a class action. I recently discovered that I had unknowingly entered a similar agreement, with a vendor who was committing widespread fraud (for small dollar amounts each time though, so it would be uneconomical for any single individual to sue).

The fact that Ticketmaster has survived as long as it has, their legal fine print is probably airtight.

*EDIT* Yep. It's a little ways down on this terms sheet under "Disputes, Including Mandatory Arbitration and Class Action Waiver":

https://www.ticketmaster.com/h/terms.html