GPL has this idea in it: trying to define what exactly should go into that tarball. The question seems meaningful and important even for proprietary code. If so

GPL has this idea in it: trying to define what exactly should go into that tarball. The question seems meaningful and important even for proprietary code. If some authors assume that anybody modifying their code should be able to look at git commits, that probably simply means that "the preferred form of the work for making modifications to it" is a git repo.