[DVassallo]

S3 and DDB are incredibly similar. Their fundamental operators are the same: key-value get/put and ordered list, and their consistency is roughly the same.

What differentiates DDB and S3 the most is cost and performance.

They're both highly-durable primitive data structures in the cloud, with a few extra features attached.

[dgemm]

If you think of them as incredibly similar then you are likely not making very good use of them.

For example consistency is not "roughly the same" with DynamoDB supporting strongly consistent and atomic operations, and atomic update operations.

[DVassallo]

S3 is also immediately consistent unless you’re updating an existing object or listing objects.

I was one of the top users by volume of both products when I worked at AWS.