To answer your first question, AFAIK, standalone services that can be used on their own are prefixed with Amazon (eg S3, EC2, DDB), whereas services that are deeply integrated into AWS ecosystem are prefixed with AWS.
Disclaimer: I work for AWS, but this is not an official answer. What I said is correct to my best knowledge, but I cannot guarantee its correctness/accuracy.
Disclaimer: I work for AWS, but this is not an official answer. What I said is correct to my best knowledge, but I cannot guarantee its correctness/accuracy.