I remember reading somewhere (probably here) that part of the reason the railroads failed to adapt to cars was because they thought of themselves as railroad companies instead of transportation companies. Maybe github is thinking of themselves as a collaborative work company rather than a collaborative coding company and trying to adapt to that.
In the U.S., intercity railroads found they could make more money by focusing on freight and leaving passengers to poor Amtrak. If Warren Buffet's acquisition of BNSF is any indication, the private railroads are quite profitable.
The decline of intracity passenger rail in the U.S. has many causes (massive public investment in the Interstate highway system for one). Still, it's worth remembering that auto companies played an active role in acquiring and disassembling streetcar lines: http://en.wikipedia.org/wiki/General_Motors_streetcar_conspi...
I think Github is probably vulnerable to a team that stays focused on the bread-and-butter tools that are actually important to developers.