I'm against using a Madden sim for multiple reasons. As PK said, I think it adds a whole other dimension of having to study imperfect Madden ratings. Also, also Madden simulations are completely random, the best team might now win. You can't predict whether Tom Brady would throw a pick in a Madden simulation or if Ray Lewis would miss a tackle that leads to a long touchdown.
These games are supposed to be about the best team in general winning it all and the randomness of Madden would remove that entirely.