For the books you already know you want, I agree that Amazon is hard to beat. However, it’s hard to replicate the “discoverability” of a brick and mortar bookshop. Even without having a specific title in mind, I can always find something that looks interesting, just by walking around. Sometimes a blurb on the cover draws me in, sometimes it’s a recommendation by the staff, and sometimes seeing a title or author jogs my memory.
Meanwhile, logging into my Amazon account recommends several books (out of order) in a series, some updated versions of textbooks I once bought, and a few titles I recognize from the NYT best seller list but have no interest in. Since I recently bought one, there are also a good dozen screwdrivers for what Amazon assumes is my burgeoning collection of flatheads.
Also, books don’t cost very much, but they are a big investment in terms of time. Thumbing through the actual book is a great way to make sure you like your prospective purchase. This isn’t quite the same online—Look Inside is carefully metered out so you can maybe get a sense of the books style and level, but it’s often not enough to draw me in.