Don't want to dwell too much on tactics, but couldnt resist
If we play Pirlo further up, we are going to have 3 AM's: Kaka, Pirlo, Ronaldinho/Seedorf, and 2 DM's behind them. If any team plays a good counter attacking game with speed and direct balls to empty spaces (there will be plenty given our wing back's propensity to push forwards), there is no way in the world that Pirlo and any of our other AM's can make it back on time---we will be slaughtered against fast counterattacking teams. The reason Pirlo is in front of the back four and in between the 2 DM's is to add additional defensive cover, as he is essentially covering space and tracking to help our DM's or wing backs in the defensive phase.