People will not pay for service, by and large. There will always be a premium for bricks and mortar shops unless they're far out of the way, or they're very lucky with rent (Scan do ok, because they have one shop open on restricted hours, outside a retail park, and at least two warehouses to stock their predominantly mail order business).
It isn't just Maplin who stock expensive cables - almost much all retail outlets (with the exception of Poundland, and possibly Clas Ohlson ) are pricey, and that should tell you something.
Prices at Amazon are also increasing incidentally.
A lot of the more independent stores are on historic favourable rents; their building then gets re-developed, the rent doubles, and the only business that can afford it are the large corporates, leading to a sanitised high street. Rinse and repeat.