More to the point though, a 10m HDMI cable at Currys is £40, a 10m HDMI cable at Maplin is £50. If you've got time to check both, you'll be buying in Currys.
You can't compare bricks and mortar high street stores to online warehouse retailers. They're targeting different markets. By your standards every brick-and-mortar shop would be shut, because everyone would buy everything online. That's not the reality. What Maplin have failed to do is give people a reason to choose to shop there - and while part of that is price, it's a lot more complicated than that.