Someone could say that changelogs refer only to FIXED bugs and tell in most cases little about the rest and about the comments written in an internal context.

But actually I take this from a very different angle: the internal bug tracking system is a central piece of the release process and affects many teams and processes. Instead, where and how you handle your code is mostly your decision as long as you follow the steps to release it and you keep your duties with the release program. If you play by these rules, there is not a fundamental difference between a tarball released and the corresponding git tree.