I’ve always thought of version control systems and issue trackers as separate products. GitHub just happens to implement them both in one place. As others are alluding to in the comments, I’m highly skeptical of coupling the issue tracker and other non-VCS features with git. A far better solution would be to keep them decoupled, but easily pluggable and extendable. In fact, this is basically the status quo with any i…
Agreed, but coupling has extreme benefits. No matter how stringent you are on your commit message requirements, you'll never capture the scope of a code change as well as the originating issue.
They may be separate products, but the need for a cross-vendor common interface/implementation persists. Also, the ability to take your ball and play elsewhere is required too. If a git-like approach were taken towards issue management and all of these platforms could implement/use it, nobody would ask to piggy back on git. Then again, you can apply this same discussion to any form of structured, persisted digital content...nobody wants to be locked in. Just so happens that the code part happens to have an unencumbered implementation that others have embraced.