It's nothing to do with being decentralised or not. There are decentralised version control systems with better command line interfaces. Some of them even predate git. Mercurial has a better interface. So does darcs.
Strongly disagree that Mercurial has a better interface. I've worked on projects in cvs, svn, git, and hg, and I have to say I found hg's interface nearly as confounding as cvs.
Not wanting to argue which perspective is right, just that you can't make a broad sweeping statement that Mercurial has a better interface
