Sublinks in Google Results

When do Google results contain the sublinks underneath the extract? Michael Nguyne explores this in a post Traffic Determines Google UI Snippet Links. See also Barry Schwartz' post at SearchEngineWatch. I am certainly seeing more examples of these sublinks in Google results. Even if these guesses are not correct as to the why of their appearance, at least we now have a name for them: sublinks. See the image below: