Perhaps if they were more affordable they'd have a larger market share, what what?
Possibly. They have a fine balance to strike, what with being the only wargaming brand (that I'm aware of) with a high street presence across Britain and (to a lesser extent) internationally. They've been having problems financially of late, what with the cost of the necessary high street presence (as opposed to online retail) and the economic downturn making people cut back on luxury goods, so they've rolled out new products, and closed a few stores, IIRC. I know quite a few of their products are more expensive than comparable ones offered by similar companies, but those companies don't have to maintain a high street presence and often aim at a related but slightly different demographic.
In terms of shopping, if GW were to sell anything other than their branded products, they would have to sell it at high street prices. I can get them cheaper online. In fact, I can get GW stuff cheaper online than in their stores via independent retailers. But GW offers more than just models. They provide gaming facilities, painting tuition for beginners, advice on playing the game. That's their hook. Get kids in to see the shiny stuff. They can sell for less if they dump all the high street stores, but then the kids will be stuck with kitchen tables, and won't get told how to paint, &c, &c. People do end up paying through the nose for branded paints and glues, but they do seem to be prepared to do so for the prices GW charges.
In short, they are a business, and they do a pretty good job of keeping prices at a fairly reasonable level, given what the company as a whole offers across its customer base. But I honestly don't know the minutiae of whether they could increase their market share by 10% if they had a 10% drop in prices.