Why does a DVD from Harrods cost so much?

There are few places i can say have the prestige that the Harrods chains have. Specifically the one in Knightsbridge, located somewhere in London. There are also few places selling the diverse range of foods that Harrods sell. Yet, I have never come across such high prices for such a shop. Recently whilst visiting, i noticed that the SALE price of the film, "the Water Horse" was nearing £15. The same price that every generic chain hypermarket do for almost 5 pound cheaper. Now if you have read up to this point, you are probably thinking something overtly intellectual, something along the lines of they put the premium of the price even higher so during the sale, their still making the same amount of money as our supermarket chains are. There is also a prestige to going to Harrods, if you happen to have bought a Harrods bag (50p where sold) you can now consider yourself almost nearing posh, and yes the jewellery is bedazzling and the cars are bloody brilliant but is it really worth buying from that shop? i somehow dont think so.