The reason is that retail stores don't have the space to store products and it's expected by the consumer that when you walk into a store products should be in-

The reason is that retail stores don't have the space to store products and it's expected by the consumer that when you walk into a store products should be in-stock. All inventory at a retail location is supposed to be just-in-time and for the area that they service so they do not support the warehouse model. Store like Hot Topic here in the US have been shipping from stores for some time and the idea behind this is that both warehouse and retail adhere to the just-in-time model. That way product is no more likely to sit in a warehouse than it is at the retail location, there's no ship backs and markdowns are taken at the retail location. As a result inventory stays fresh and there's little to no overstock. This does not work for all retailers as you can imagine, for for boutique stores with a limited number of SKU's it's enough to keep them afloat while still turning inventory and keeping retail locations staffed.