I've read this elsewhere as well, but this is the best website explanation I could find. This is what occurs in the States, though it probably extends to Europe, too. http://www.coreylevitan.com/features/ticket.txt
"Fans tend to blame concert promoters. But it's
the artists who have final say on a ticket's
price. Promoters enter bidding wars to secure
rights for each major tour, competing to promise a
minimum dollar amount the artist will earn for
each show. (These guarantees mean that in the
event of disappointing box office, promoters
shoulder the loss, not the artist.)"
A paragraph or two later..
"The artists realize that (high guarantees)
translate into very high ticket prices if they
take the money," Bongiovanni says. "If they're
concerned about the ticket price, they always have
the ability to say, 'I want my tickets to be no
more than X.' But at this point, most artists are
just taking the money."
Basically, the artist says how much it wants for a show. The promoter then finds an appropriate venue, does the math to see how much he has to charge to pay the artist his guaranteed money and to make a decent amount himself, and then sets the price. If Queen fails to sell out a venue, it's the promoter who might be out money. High ticket price - artist wants more money upfront; low ticket price - artist wants you to eat for the next month.
Now, as if you can't tell by now, selling tickets in Prague for 35-70 Euros, while selling exclusive tickets to hardcore fans for 55 pounds, is odd at best, fleecing at worst.
DJ's the man we love the most