When I run the following on a command line:
I get different results than if I choose the following menu option within Android Studio.
Can anyone explain this? Is this normal? Should a prudent developer run both in order to find all potential problems with his/her project?
In Android Studio you can customize what inspections are run via Preferences > Inspections; you may have some Lint inspections disabled, and not all run by default. Android Studio can also run a great number of non-Lint inspections.
You are running two different tools. The command:
$ ./gradlew lint
runs the lint tool that comes with the Android SDK and the menu option
in Android Studio is a feature inherited from JetBrains IntelliJ IDEA which runs:
<android studio path>/bin/inspect.sh