Which is not true. Little green lock means the site has HTTPS, being safe requires much more than that. Security is hard to explain.
I even wonder how many people download an ISO or installer from a website, and do any sort of due diligence to find the signer's key from another 3rd party location, then verify previous builds, or require multiple signers of a key to give any semblance that the key is not fake? Or do we all just download the ISO and the .iso.asc file from the links provided and call it good? Even security minded people can be lazy in this situation.
Another reason HTTPS is easy is that it uses a centralized trust model, relying on CAs to vet each website.
GPG is neither. It tries to provide encryption at rest, and relies on a web of trust that we cannot reasonably expect everyone to operate securely.
Then you update your system (maybe after a prudent 3 week wait) and everything works, except the GPG Suite, and you can't send encrypted emails for a while, nor can you read ones you receive, or old ones stored locally.
(For macOS 10.12 sierra, released 2016-09-20, there's now a beta of the GPG Suite, released 2017-01-23, 4 months later.)
There was also a bug (or feature?) a while ago where email drafts that you had open in windows would vanish after a while.
It is a good solution for the Mac, but this is something to be mindful of (and it sort of supports the main thrust of the article).