In actual fact retailers are under no legal obligation to take back your old goods and dispose of them for you. They have the option to fund civic amenities so that their customers have somewhere to take them to for recycling. I used to work for a well know office supplies store and this was the action they took, and I am sure most other retailers have as well.
Although we did also have special offers on throughout the year where we would give healthy discounts on new printers and/or routers (1/3 off £300 machines in some cases) in exchange for the goods they were replacing which we would personally send off to be refurbished in possible and recycled if not.