As a software guy, rebuilding many of the features of Amazon that users love isn't awfully hard or expensive.

I think it's a unique combination of logistics and tech which few companies manage to successfully pursue. Things like hooking up the cash register system to the website so the website doesn't say "in stock" when someone has bought the last one. It's pretty easy for someone techy to do that, but there is rarely a sufficiently techy person on staff in a typical small business.