What gives you that idea? I run several cronjobs that deal with their service, and it's down a lot compared to other similar services. My jobs deal with that gracefully, but if I wanted to I could easily set up a more reliable service than GitHub if my only goal was to host *.git repositories, not have any of the other nice things they provide.
And the fact that they have somewhere north of 5 terabytes of active data, and their job queue is handling many hundreds of thousands of jobs a day, and it pretty much all happens extremely fast with nary a hiccup. I know there are outages, but I'm pushing up changes to them something like 10 hours a day every day, and I've never noticed them.
They've struggled and dealt with a number of hard engineering problems, which they've blogged extensively about. In particular, their architectural (both hardware and software) changes since leaving Engine Yard demonstrate more than a simple "working knowledge" of how to build large-scale systems.
What gives you that idea? I run several cronjobs that deal with their service, and it's down a lot compared to other similar services. My jobs deal with that gracefully, but if I wanted to I could easily set up a more reliable service than GitHub if my only goal was to host *.git repositories, not have any of the other nice things they provide.