The Erlang team uses ClearCase internally and decided that a full-history conversion to Git would be too difficult to be practical, which is why they are starting with a single commit. According to the official Erlang website:
Beginning with this release we will maintain (and update on a daily basis) a
GIT repository on GitHub. The intention is that this will make it easier for
users to contribute with bugfixes and new functionality and also easier for us
to receive the contributions.
We (GitHub) worked with the Erlang team to make sure we could provide the functionality they desired to make their bidirection Git mirror widely available and to streamline the patch submission process.
I'm sure the team will further discuss exactly how this new Git repository impacts Erlang developers wishing to submit changes. Everything I gathered from our conversation with them makes me believe they are dedicated to making this new process work for the Erlang community and I'm excited to see the development of Erlang/OTP accelerated because of it.