Based on my experience, that information and some of the comments about it in the thread are out of date or inaccurate.
'Move to AWS' was a program focused on accelerating AWS adoption that was primarily active something like 5-7 years ago. The program achieved its goals and concluded: virtually all infrastructure was running on AWS. I worked on the program for part of that time, in the last couple of years it was active. Amazon's migration to AWS was was covered in a 2012 presentation at AWS re:Invent: "Drinking Our Own Champagne: Amazon's Migration to AWS" [1].
Some more recent efforts around AWS usage were covered in a 2016 talk: "How Amazon.com Uses AWS Management Tools" [2] (which references the earlier talk and discusses some of the changes since then). There are ongoing projects to improve and optimize usage of AWS, as well as to adopt some of the newer services.
[1] https://www.youtube.com/watch?v=f45Uo5rw6YY [2] https://www.youtube.com/watch?v=IBvsizhKtFk&t=13m20s