For me, it's not that local retailers don't have the merchandise. The reasons i buy online are:
1.Easier price comparisons mean its often cheaper to buy online.
2.No hassle from salespeople or with uninformed salespeople.
3.The lack of sales tax generally pays for delivery charges if any.
4.CONVENIENCE. I don't have to drive to the store, find a parking place and fight the weather or crowds.
The nearest decent bookstore to my house is a Barnes & Noble in Idaho Falls. That is a 50 mile trek north and the inventory isn't all that good. Even with the annual membership, I'm in a losing position after paying for 100 mile round trip, local sales tax and a poorer overall discount than I could achieve with a direct online purchase.
I enjoy my business trips to the northern Virginia area. The Borders book store on Route 7 near Tysons Corner has a pretty decent computer section. I often make a purchase there and cover it by underrunning my food per diem.