It made more sense a few years ago when there weren't distro centers near most major population centers and 1hr delivery options. Pre-shipping isn't going to be 1hr by much!
Maybe that's how they've implemented 1hr shipping?
No, they just have urban area distro centers with commonly ordered products that would be desired quickly. Here in Seattle it's an old car dealership that's right near downtown--tons of space for delivery cars and enough for popular SKUs.