Re: How can it possibly be worth that much?
I'm the AC in the 50k+ employees who posted the numbers earlier.
When we were setting up the GitHub, I had a chat with one of the team who were managing the roll out. Asking things like why GitHub etc.
Bearing in mind we have several DCs around the world (2 or 3 depending on region), so we have places to host our own services and the expertise to do this ourselves. Git itself itself isn't difficult, but obviously it needs hosting, it needs resilience, security (this is for internal commercial projects, not Open Source). etc etc.
Bottom line was cost. Once you took into account that someone would need to build and maintain this, and it was being rolled out to all developers in our org, so needed to scale etc. It turned out far cheaper per head to get Enterprise GitHub, with a floating license, than it would have been to do it ourselves,
Plus most of our developers were already familiar with GitHub, due to people contributing, or just looking at, Open Source projects, so there was no real learning curve, just an email saying you now have Enterprise access to GitHub.