I'm not so sure. I believe Amazon customers are getting a push notification on their mobile device for every delivery notification, which leads me to believe (at least in the case of Amazon) they have the data.

Yeah I am pretty sure Amazon works with most of their shippers because you can usually see all your shipping status information right in Amazon itself without having to leave Amazon to go view it. And like you mentioned there also are delivery notifications.

In fact the shipping company Amazon typically uses in my area takes pictures of their deliveries. So I get an email from the delivery company with a picture, but then Amazon also allows me to view the delivery picture on their site too and notifies me of the picture.

With how much server power Amazon has, I can't imagine them being afraid to make some API calls.