I see the wisdom in what you are saying bodie, and I am a big detractor of those that manage "robotically" as you so well put it. I've been mulling this one over the past day or so, and I was about to side with your argument until I read this:
True, but then you will ***** your setup guy to pitch two innings (which isnt the norm) and then the next day your in the same situation, but your set up guy pitched 2 innings the day before. Then you have to use your closer for 2 innings. When only pitching 1 inning a game it allows the pitchers to stay fresher and pitch 3 or 3 games in a row if need be.
I hadn't even thought of what Magnet is saying, but I have to agree that it is a convincing argument for doing things "by the book". If you are going to have a specific setup man and closer, I think you have to do it by the book and use one for the 8th and one for the 9th. In cases of teams that don't have a specific set-up man (of course very rare nowadays), then I can see extending the setup man for an extra inning, because you can come back the next day with a different setup man.
If you overextend the setup man and he can't pitch the next day, then you risk the scenario of either having a middle reliever working into or for the 8th, or you have your closer pitch 2 innings (as Magnet said) overextending him, and then you lose him for the next game. The fast-paced game after game scheduling of the season dictates that you sparingly use your best relievers so you can count on them to be in every game if need be.