I actually prefer Zambrotta on the left side of the pitch, for tactical reasons. Camoranesi covers the right flank attack-wise, while Nedved tends to cut in from the left to the middle, leaving room for Zambrotta to attack. You could do the same on the left with Chiellini, but Zambrotta is still the better player.
Not to mention, defensively the right flank would be a risk zone. It would have a huge chance of being open and weak to counter-attacks. A defensive rb is better when the lb is attacking.
Keeping Zambrotta as left-back would make for a more balanced side.