It was just as offside as Trez against Torino was.
Both were correctly allowed.
Not exactly the same, Red.
In La Domenica Sportiva they compared the goals and the referee there (Tombolini i think) said many times how there is a difference. The ball was passed to Di Natale, who was offside previously, by an Udinese player while the ball was passed to Trez by a Torino defender.
I think Colina was also present when they were discussing these situations and even he confirmed that Di Natale's goal should have been disallowed.
Di Natale was in pasive offside but he was directly involved in the action all the time, when the ball was passed forwards and when the ball was passed to him. While in Trezeguet's case it was different because the action was stopped by Torino's player and he started a new action when he passed the ball to Trez.
I don't know if this is exactly what they said but it was something in this context.