AFAIK, Netflix doesn't use Amazon for delivering streams to their customer (they use Level3's CDN). They use Amazon for batch jobs like transcoding and to host their API servers.
Using Amazon for API servers is a little surprising, btw. I would have gone with dedicated hardware. Maybe the sheer number of machines for API service is so high that using AWS APIs is a significant saving in operations complexity?
Netflix uses more than one CDN, and, according to posts by their one of their architects (Adrian Cockroft http://perfcap.blogspot.com/), they use EC2 for everything but some basic in-house HR/backoffice stuff.
He's got DOZENS of posts on how it works for them, how they full embraced ec2, etc. and how well it's working for them.
Using Amazon for API servers is a little surprising, btw. I would have gone with dedicated hardware. Maybe the sheer number of machines for API service is so high that using AWS APIs is a significant saving in operations complexity?