They cost far too much for me personally, but that's irrelevant. The tickets are worth whatever consumers are willing to pay. The fact that these shows are always sold out suggests that the prices may be well below market clearing. They could get away with increasing them further, and those who can afford it will still pay. For everyone else, there's YouTube.
As a concert promoter, I can tell you that there are a lot of background costs that most fans and ticket purchasers to not take into consideration.
Take an average sized gig, a thousand a few thousand in capacity for example. You have first off, the promoters costs, working over months to put the concert together. You have the venue hire fee, which will include covering there staff, general venue maintenance and licence fees along with needing to make a profit on their part. Then you have your own staff costs such as security, sound guy, lighting guy, door staff, bar staff, cleaners, first aid, people to take care of the bands, accountants, pr staff, steet team members etc. After that you have your band costs, the bands them self have to cover their own expenses of travel, equipment, pr etc. As well as living costs while on tour. You then might have equipment costs in terms of sound equiptment (desk, leads, mics etc.), you have admin costs, things like door stamps, contracts, printouts of info for the bands that night, e-mail and phone costs for keeping in touch with the bands etc. After all this, you stil need to advertise, this entails printing costs of flyers, posters, sometimes even billboards, and with all that, graphic design costs. Also magazine listings, radio listings, online advertising etc. After that, ticket costs, if your venue has strict 18+ policies you might have wristband costs depending on how they work things.
And after all of this, you need to make sure you have covered your risk. For, by all means, you could shell out for all of this, and if you made one mistake on who you picked to play a show, you could make a loss on every single front.
For those reasons, no. Concert tickets, in general, are not over expensive.
Oh, and this isn't going into the side of bands who charge £1000 for their rider, or any extras like that.