I can't decide if it's a ridiculous mark-up or not. Display packaging, boxing up, staff time ordering, displaying, restocking, selling etc. All mounts up. Presumably when shops do half price sales they're shifting stock at cost price just to clear their warehouses and stock rooms so I guess not. TI will be relying on low overheads, buying in more cheaply and shifting high volumes on low mark-up. And they're adding 25% for transit, which is already contained in the shop price. Hmm. I guess not then.
Thinking about it, it's probably people like Wiggle and CRC that have ridiculous mark-ups. They'll be buying very cheap and have low overheads but their prices are only lower, not generally half the price, of shops.