The prices during the closing sale at my Borders location (Anchorage, AK) never offered that great of value except with the magazines that all went 50% off. Most of the rest of the books rarely excceeded 30% off and that pretty much put them at Amazon prices, and still well above the local used book store.
Ultimately big-box book stores are squeezed between the used book stores and Amazon, both of which offer lower prices.
I try to avoid Amazon, it's like the Wal-Mart of e-commerce, but sometimes the price difference is too much to ignore. 40% cheaper prices with free shipping? Hard to pass up. Still, I buy from brick-and-mortar stores whenever I can because I don't want them to go away.
I have to add that months after our Borders closed, the local Barnes & Noble is doing a very brisk business, noticeably higher than before. There are now only two book stores in the city - B&N and a large used book store.