Saying that Milan scores in the last minute because 'they want to score', while Juve 'sits back' is simply nonsense.
I think that what you are trying to say is that the squad lacks fighting spirit. I strongly disagree with this. Does Emerson have fighting spirit? Cannavaro? BLASI?
The reason that Milan scores more often in the later phases of the game is because Shevchenko is a superb striker, and Kaka and Pirlo provide enough creativity/passing so that they can force an opening in the opponents' defense. Juventus however attacks more slowly, but with much better teamwork. To quote Cannavaro: 'The difference is, that at Juventus, we attack together and we defend together. We do not leave each other to rot.'.