per wikipedia, it looks like amazon's current fleet is 66 aircraft, and prior to this news had already ordered 15 additional 767-300ER. https://en.wikipedia.org/wiki/Amazon_Air
As the other poster noted, these are the first outright purchases of planes, vs previous planes were leased from aircraft leasing companies. My understanding is that when you lease, the leasing company handles all the maintenance and crewing and you only specify the routings. Obviously when you buy planes, you're responsible for everything yourself. You can however contract out maintenance and crewing to other contra…
Airlines are more likely to buy packages of service from manufacturers (especially engines) and big service providers if they don't have enough scale or experience to do their own maintenance, regardless of how it was paid for.