It's too bad he had to wait until he was 30 years old to showcase his all-around game!
I take it you only started watching the Celtics this past season? 
uhhm acutally Paul Pierce never played defense b4 this past year as good as he did this year. He changed his whole technique on defense this year. Paul also used better footwork on offense this year too. His passing and unselfishness was also more pronounced this year becuase he has better teammates.
Pierce started playing his all around game in 2002-2003 when defenses started solely focusing on stopping Paul Pierce. It was never more evident the following season when Paul averaged a career high in assists with 5.1 per game.
Since then, Paul has never averaged under 4 assists per game. Paul has always been a gifted scorer and a tremendous rebounder from the 2 or 3 spot.
Pierce also started making a commitment to defense at back half of the 2000 season when Jim O'Brien took over.
I want to say that because the team won so many games this year and because of the 2 additional star power players joining this team...every was magnified for this team and its players, thus Pierce's defense was far more recognized this year than previous years.
To the outside, casual follower of the Celtics and Paul Pierce, they would only assume that Pierce, this year, only started to play good defense or any defense for that matter.
But to a true follower of The Truth, we know he was always a good defender and played good defense, but sometimes the focus just wasn't there for the team, as a whole, to play good defense.