Git is a distributed version control system. This means that every git clone is a full repository with complete history and revision tracking. Git differs from Subversion because Subversion has one central server and the clients just commit to it. This is why git is so much easier to use for ‘social coding’ and that is where Github spawned from.
This is why I prefer to use git and Github for the source code management and use the WordPress svn repository only as a distribution channel. That works for me, easy to use source control but also a distribution channel that’s accessible to the users. WordPress try to make you solely use Subversion – but you don’t have to!