Article author here. So, you're right that while AWS does continue to lower prices, they're still not the cheapest game in town. Frankly, they're not even necessarily the most performant game in town.
What they are really competing on is breadth and depth of service. The article goes into a lot of those services, but, as one example, if you launch an instance in EC2 you can allow it to access secured buckets in S3 without any need to store keys/passwords on the instance itself thanks to IAM roles.
Another example is services like AWS Lambda, which is a hosted way to run a function without any need to manage servers.
The list goes on and on...direct VPN connectivity, Hosted Active Directory, CloudHSM. While I'm biased, my perception is that AWS is pretty far ahead of the pack.