Why would it not be their goal to abstract away the pain? Sure, you still have the power of git available to you, but not everyone who uses Github may want to learn git. They may simply be looking for versioning of their assets (images, geojson, etc).
And I personally couldn't be happier; most of the projects I'm involved with use Mercurial. So to me, git's interface is difficult to understand and foreign despite my own efforts to try to lean it.
GitHub and SourceTree combined have taken all the pain way from me using git.
