I am assuming here guys so bear with me. IF the announcment by Moggi was made after the TIM Cup, then I think it would be reasonable to say that Juve felt pressured to rush the signing in order to instill some belief in the team and the fans. That could be the reason why the announcement was made tonight before it could be made official. This could also be why we ended up paying so much for Emerson.
Another wild theory is that Moggi might have announced this without even having confirmed the deal with Roma yet and this might be his way of letting them know that he is settling for their price. Which could mean that no official agreement has been made at that meeting but Roma did table their offer and this was Moggis way of accepting(under pressure of course).
He might have been planning to bring them down more. But then maybe Agnelli made a phone call after the TIM game saying something along the lines of, " Bro, we playing really crap, buy Emerson tonight, I dont care about the price, cheers."