The Mac Observer:

For the purposes of Gatekeeper, Apple verifies the identity of the developer, but not their intent. It’s up to you to ensure that the applications you install and run on your Mac come from the people you think they came from, and we’ll show you how to do that.

The key words are, “it’s up to you” to not let your guard down and to always be aware of what you are downloading and installing. Apple is doing their part and it’s up to the user to do theirs.