The problem with the u21 is that no-one can read the game the way he can. The others aren't even close to him.
So he has to adjust to the others and make more simple passes. I noticed that whenever he tries to do something more complicated the others can't read and predict what will he do so sometimes it ends up with a lost ball, eventhough what Gio was trying to do was genius.
When Rossi is playing it works much better because he complements Giovinco better than the other youngsters.
Now, just imagine what will happen when he'll have Del Piero and Camoranesi in his team.