Actually in some cases 'base' isn't always same as 'our'. Because in Git Model we are comparing commit vs. commit. This means that most comparisons will be done 'our' vs 'our' commit (that are commit that was made by user in theirs topic branch) or 'their' vs 'their' (in this case that are commits that comes from remote repository). There would be only one commit that can be described as 'our' vs 'their', this will be a common ancestor commit.

But this is only my humble opinion ...