It hasn't completely obliterated all the competition, but most of it, and those that aren't dead are on life support: in the open-source domain, CVS is mostly dead, SVN isn't far behind, and Mercurial is barely hanging on. In the proprietary domain, it seems only stodgy long-time enterprise customers still use Perforce and ClearCase, and MS's SourceSafe seems to be dead (and MS even bought GitHub).