Hahaha, that's a very good point Maurice! Although in fairness, I think the Smiths songs with Finn etc are just a whim, a bit of nostalgic indulgence on Marr's part - they don't have any real significance beyond that exact moment.
Bring Morrissey into the equation and it's a different ball game entirely; the songs represent the history, the friendships, their very lives at the time of writing. Marr said to Morley in that very interview ^ that he can view "The Smiths" almost in a detached light now, as though he were not involved. I very much doubt he would be able to do that if he were stood 2 feet from Morrissey, hearing him sing "There Is a Light...", which is most likely why a reunion will never happen.