It seems to me that the git/GitHub owners, by assuming that there is only one use-case for git/GitHub (shared open software development), are limiting the usefulness of GitHub. Some of the postings in this thread show other use cases that require readonly access to files for one audience yet require pulling/pushing/versions/branches to the developers.
An additional use case that occurs to me is using GitHub to make a portion of a proprietary product public. We always assume that a product is either proprietary or open, but not both. But I can easily imagine products that are proprietary and sold for profit, yet contribute a new and useful subroutine or algorithm to the Open Software community. In such a case the developers might want to use GitHub to collaborate in private, but might want one specific file to be readonly or read/write visible to the public.