The list of blog post elements on page 86 of the user manual has somewhat unfortunate choice of words. You are completely right when you say that it implicitly sounds like there is a trackback system in place, nevertheless we don't have this feature implemented yet.
At the moment being I can't specify precisely when we are going to implement this feature, but we are surely going to look at it after Sitefinity 3.1 is released.
Please accept my apology for the misleading content of the user manual.
the Telerik team