Why should large financial/insurance companies use git and/or github

Question

I work for a large enterprise (30K employees) in the financial/insurance industry. While "IT" isn't our main focus, let's be honest, these are information driven industries and the companies with the better technological advantage seem to get ahead faster.

There are many software development teams at my company. They are all over the map with version control, let alone languages/frameworks used. Some don't use any (I know), some use PVCS, some use VSS, and the most enlightened use SVN.

I want to bring git to my enterprise. More specifically, I want to bring GitHub (private repositories). I know the right people to talk to about this, but let's be honest again, drastic moves like this usually get shot down in the large enterprise setting because of vague security concerns or the fact that none of our competitors are using it (and I can only cite jQuery, Ruby on Rails, Facebook, etc as references).

So my question is this. What are the most compelling reasons of why a large enterprise should slowly and deliberately make the switch from PVCS/VSS/SVN to a hosted git solution like GitHub (private repo). Of course, part of my plan involves a POC for a non-essential development project.