Take a look at the Eventbite fees here - http://www.eventbrite.com/fees/
I think they're totally reasonable. I'm not going to get into specifics that would expose our finances, but I'll say that we have a lot of people behind the scenes taking care of building and maintaining the product on both the organizer and attendee facing side. On top of that we have some excellent customer service people who take care of hiccups and guide users in their time(s) of need. All those fantastic people need to be cared for (ie. paid).
If you're asking about the general perception of ticketing, I'll refer you to an article in the LA Weekly. http://bit.ly/1kAT1K0 (tldr; There are existing patterns in particular industries to deflate the perceived ticket prices, only to inflate them at checkout.)
There's a brief clip explaining Eventbrite fees here: http://bit.ly/1f28hw6
Hope this clears things up a bit.
