Cassano made his debut in the Emirates Cup win over Al Ahli this week.
Berlusconi said: "I am sorry for Ronaldinho who is the greatest player in the world with regard to speed of thought and execution, but it's his decision to return to Brazil.
"I am very happy with the arrival of Cassano who is the greatest Italian talent.
"A winning Milan does Italy good. Milan's players have the responsibility to win, first of all because this way they are happy and also because it makes the club, the fans, the President and even the politicians happy.
"When Milan win you see smiles in parliament, so a Milan that wins does the country good."