The fact that Argos are pricing themseleves out of the market for stock which has to ordered anyway would indicate a reluctance on the part of Argos to actually want to sell that product in the first instance. There could be all number of reasons for displaying the products, not least the fact that Meile will be paying a small fourtune to have their advert in the Argos book.
This is where retailing works in reverse. Under normal circumstances, chain stores like Argos buy stock from a manufcaturer or supplier for £X and then sell it to the public for £Y. In doing so, they make a % profit. However, for every sale of product A, it is a none-sale of product B, C, and D.
Product A may have a larger retail price than product D, but that by no means equals a higher profit margin. The profit is of course the difference between price £X and price £Y, once all expenses have been taken out.
So, in the case of Miele vacuum cleaners, it could well be that Argos would rather sell other, cheaper cleaners, as profit margins may be greater. But if Miele are willing to pay Argos a vast amount of money to advertise in their book and on their website, Argos could well stand to make far more profit from that arrangement than they might by selling a cleaner itself.
Thus, the whole idea that Argos "sell" Meile cleaners to make money in the usual way could well be a white-elephant in the sense that the retail price is too high and encourages consumers to shop elsewhere. Argos make money from Meile by using their book as little more than an advertising medium. Meile get the sale from which ever retailer it is that the customer chooses to use. It's a concept which is incredily hard to understand if one has not been involved in the retail business, but not everything you see on sale is actually there to be actively promoted.