to be fair, he was essential in juve's first scudetto...
he bring calmness in juve's young midfielder (marchisio and vidal)
not to mention He made the most assists in the Serie A that season
Absolutely, in the first season of Juve, a player like Pirlo was very needed ... they had a lot of hard-working players but not a lot of players with his talent. To be able to pull an assist from a deep pass, a goal from a free kick or a good pass from a corner or free kick were all things that Juve needed. What Juve had plenty were players that didn't mind running (e.g. Giaccherini) .
Plus in his first year, he was trying to establish himself and like so many players (Robinho, Boateng, Diego, Krasic, etc) he started very strong.
In hindsight, considering all our injuries and performances of some players, letting go Pirlo turned out for worse, but at the time it looked by far the best decision (Van Bommel was playing great and Pirlo was not justifying his high salary).
He'll always be part of Milan history, but I don't feel the same level of affection for him that I have for many other Milan players during that time (Nesta, Gattuso, etc). Though if I was in his shoes, I might have ended up taking the exact same decisions. Soccer nowadays is a business whether we as fans like it or not.