True, I myself believe I chose the title wrong but I only realized after this comment. I met the main developer who created the Ruby wrapper for aws-sdk a few days ago and I was really surprised how it works so similar to ActiveRecord that I thought that this was new. The code is on github and I didn't find any similar overview of the aws-sdk for Ruby on Rails, so I thought this might be helpful.
I'm not sure, but from reading the article this feels more like AWS-SDK's seamless integration with Rails rather than Rails' seamless integration with DynamoDB & S3. Please correct me if I misunderstood.