Nice horseshit hypothetical there. Keep reaching.
Yes, you are changing it from year to year, but only because relieving is more stressful. Whether he's throwing in relief or starting, he's still throwing a baseball, you get that, right?
We don't play Ortiz at first not because he's the best DH, but because he has a history of knee problems and his defense isn't necessarily spectacular. We know that, though. If we didn't know it, it would be stupid to not try him there. Same thing with Papelbon.
Rivera isn't a closer if he made it as a starter. Papelbon hasn't failed as a starter yet. Not trying him there is wasting the chance to know if he can provide the ultimate pitching value. And, once again, nothing is precluding them from having him relieve after 2007 if he doesn't make it. Choosing to start him doesn't eliminate the option of having him close in the future, no matter how much you stamp your feet about it, that option just doesn't go away.