Some ticket agencies in London are just as bad as touts. How can they charge £100 for a £25 ticket? They may as well just stand outside the venue and sell them there. Like you say, as long as people are paying the stupid prices then they will continue to do so. I really don't know how they get away with it.
I am one of the lucky ones that got tickets but if I hadn't I would just accept it and wait for the tour...there would be NO WAY I would pay 4 times the amount that the ticket was originally selling for. Some people are paying 8 times the amount!!!