Well the recommended hostname to be used to hit the Docker Hub registry is registry-1.docker.io and the recommended hostname to hit Docker Hub UI is hub.docker.com. I said legacy, but I realize these were based off of passed down knowledge throughout the years at Docker without being documented. Thus all hostnames are still valid, but we will be looking to officially document the correct hostnames to be using for all of our products soon.
Sorry for the confusion and inconvenience.