First of all, I didn't say that any of the reasons I posted were THE reason, only some possibilities. I only wanted to point out that it's easy to sit back an criticize without having all the facts. As I said before, unless you've walked in their shoes you really have no idea.
As for the examples such as B&H, Campmor, etc., those are big operations and a LARGE portion of their business is mail order. So again, volume pricing applies and they operate on a whole different scale of economics than a small, privately owned store. You can't really compare the two.
The theft % applies here too. If a small store owner, which typically has less than 10 employees, is experiencing 80% of it's theft from said employees, they are either very good at stopping shop lifting or have hired the wrong people. Also keep in mind that these stores don't have high-tech security, surveillance, and "loss prevention departments" staff, so loss from shop lifting may well be higher.
Also, it's not just books that Amazon makes cheaper online. They sell nearly everything now. There's whole websites dedicated to finding deals online. There's phone apps for finding deals online. Even apps to where you scan barcodes of something you see in store to find the cheapest deal online. So if you think that people don't expect online prices to be lower, you're fooling yourself.
The Walmart example is a good one. Where I live there's a Sam's club right next to Walmart. Sometimes a certain item in Sams Club are priced higher than next door, which is the opposite of what you expect. Frequently you can find items at their website for even less. Best Buy is another example, they offer quite a few deals online that are not available in stores.