Not really... Amazon uses third part courier and logistics companies. As do FedEx, UPS, HP, Dell, and most major corporations with a service time guarantee. They pay a company to have a warehouse full of parts, and when one is needed, they pull it off the shelf and take it to the destination. That's how they get four hour response times on business critical server hardware, for example.
As to why they do it for blue areas instead of red, it's simply a matter of population density. Below a certain number of people per square mile, it's just not cost effective. There won't be the logistics or courier companies out that far, because again, no $$$, so they'd need to create their own warehouse of stuff that they fully controlled. Not happening in a widespread way. Pretty much any product that doesn't have a Prime 2 day guarantee is coming from a non-Amazon seller (marketplace) or it's a really niche, rarely ordered thing.
All that said, in the last 10 years or so, there's been a steady erosion of Amazon customer service and now the 2 day Prime shipping really isn't guaranteed. As recently as five years ago, if you ordered something with Prime shipping and they thought there was a hitch in the shipping, they would send a second one from another warehouse. You generally got to keep both, if the items were under a certain value. That just isn't happening any more.
Agreed...Amazon has really slipped...though I think a lot of that has to do with more and more independent vendors shipping their goods directly...
For pet supplies though, nothing beats Chewy's...it like they read your mind and the package arrives almost before you order it...
