Leak is the wrong term, and it’s doubtfully a deliberate marketing move either. More like, “suddenly being noticed because a bunch of GitHubbers followed the @AtomEditor account on Twitter”.

Also, despite the plethora of repositories, the actual editor is not available. It could be many of the public repos are public so they can be installed using their Atom Package Manager, which would likely have to jump through hoops if they were private.

I'm in this camp. Have you ever been to a talk given by Scott Chacon? He demos git on Github's internal repos. It's clear that there's little value placed on keeping a feature under wraps before it comes out over there.