I am not gonna say I am not biased when it comes to Del Piero. I want Del Piero to play in the national team because I enjoy watching him play and the WC w/o Ale won't be the same.
That is said, I do trust Del Piero and his ability to lead and win games. Yes it is true that this season hasn't be so spectacular for him, mostly due to his long injury and hideous team performance, and yes it is true that his performances with Juventus are better than the national team. But the reason is simple. When Del Piero gets to play in his position he always excels. Most of his bad games were when playing off position and was not given time to adapt.
Another reason to call in for DP is that Italy has failed to produce quality youngsters capable of carrying the torch (partly because they weren't given enough chance by their clubs to play).
If it was up to me, I'd include all of DP, Totti and Cassano in the national team.
That is said, DP did not have an AWFUL season as many have said. During most of the games he played he was top two or max three players in our squad. I know that is hardly an achievement lol, but in many games he was the best player. He is a forward that does not get service and when drops back to create he finds a midfield that doesn't move, worthless fullbacks and a hopeless forward.