Marchisio is not a starter for Juventus like Molinaro is. And, he is a starter for the u-21 side and I'm pretty sure that he would be considered for the NT as soon as he becomes a starter in Juventus. Molinaro has been a starting player for us for 2 seasons and has still never been considered for the NT under Donadoni or Lippi. They don't rate him cuz he is shit.
JCK,
Haha, JCK, I didn't expect less from you. Anyway, first of all Del Piero is considered for the NT, but really, are you comparing Del Piero who has served Italy for many years with Molinaro? Trezeguet is not a starter at Juventus and is honestly not good enough for the French NT but then again when he was a starter he was playing for the NT team for many years.
Juventus is the biggest team in Italy and if players make it in the starting eleven then they should be considered for the Italian NT. It's like Spain, if a Spanish player is a starter for Barcelona then he is definitely going to be playing for the Spanish NT.