Thanks for pointing this out to me but again its a read only code. But then again I wanted to know why is it maintained only by a few people and why it's not on github for people to see and contribute. I guess I was looking for a theoretical answer.
Base R does accept submissions (hence the periodic updates which are not all from the core team), but it is far more conservative than the typical github-type collaboration.
github also happens to be a commercial company, now owned by Microsoft. I'm actually surprised at the extent to which it is used so extensively and unquestioningly.
For an open source product github being owned by something shouldn't matter. But its nice to know that people do post submissions to the original code.