I can see reasons where you might continue to use SVN if you had been using it for a long time. Especially in a small company or coding circle, the transition from SVN to either git or Mercurial, when you might not be using any of the more powerful features of them, might make you adverse to making the switch. As pointed out by Thilo, a large company using SVN is going to find that change monumental.
Also, I think SVN still has is places, particularly when it comes to teaching revision control. But that's taking from my own personal experience of learning SVN in university versus teaching myself git, so my opinions won't be objective on that.
That being said, if you were starting a repository from scratch, I can't think of any conditions where you might decide SVN is absolutely necessary. Perhaps when dealing with legacy systems.
or legacy users ;)
