heres my thought on the matter:
Perrota nad Zanetti are essentially defensive players, considering rambo (zambo) is attacking, and the advanced quartet (bobo, totti, dp, camo) are not defensive in the least bit,it kinda makes sense to offer densive stability to a team that would be otherwise too attacking, perrotta isnt a shabby passer either, so there is a smooth transition any way.It also allows pannuci and rambo to make runs as they offer good densive cover also.
Pirlo and gatusso are a great partneship and would imo work when totti isnt playing as the team would requiire incesive passing pirlo offers.
If they were the starting lineup, we would have a very vey attacking linup that would essentially have nesta canna and gatusso offereing strenght with rambo intemetantly get caught up field and panucci is panucci.
Imo i believe italy are lucky to have the players they ahve and ofund a formation that can work wonders. Each part is integral, but i believe perrorta and zannetti are needed to allow totti and co "express" them selves.