The overpriced chocolates on the tills are the things that keep the high street WHsmith going, but like I said its not about selling stuff its about selling space. All those things that crowd the isles so you can't get a pushchair through, the post offices, the ATMs, the pick and mix, companies pay for their products to be in WHsmith at a premium price.
Added to this, if you have ever wondered why it is so dark in their stores, its because if you look at the lights, most use to have three bulbs, the figured they could save money by taking the middle one out, and then another one. Air conditioning is allowed limited use, but heating is rare (could be the other way round, I can't remember the exact law)
They have done a lot in recent times to save money because they understood that things were changing, they are shutting up shops in different towns. The worst thing Smith's ever did was sell their buildings and then start renting them back, if they hadn't done that, they would probably still be laughing.