Right, but the license attached to a file doesn't make it clear whose diffs are whose. You don't think it would be a reasonable defensive measure to include a l

Right, but the license attached to a file doesn't make it clear whose diffs are whose. You don't think it would be a reasonable defensive measure to include a license so it's obvious who committed which changes on exactly which date? (Barring someone rewriting commit history, which they could do with licenses in code comments too.)