The Facebook and LinkedIn buttons only show when you have JFBConnect or JLinked installed. Those are our extensions which have lots of integration for those social networks, like single-sign on, all the social widgets that each offers, and integration with other 3rd party Joomla extensions like JomSocial, Community Builder and more.
If you don't have JFBConnect and/or JLinked installed, the buttons will not show. The SCLogin module still works and is meant to be a good looking improvements over the default login module of Joomla. It just also works very well with our social extensions.
Hope that helps explain, but if you have any questions, just let us know.