Yes, the testing/deployment cycle for Enterprise is totally different. We usually release a major version with new features every two/three months, and 2 or 3 minor versions with bug fixes in between.
We always keep the version of github synchronized with master for development/testing, although we only release master directly in major releases. For minor releases we avoid to include major features from github to keep it as much stable as possible.
I am hoping that Github could shed more light on the how they ship an enterprise version along with the SAASy web version that we all know and love.