Ray Allen going berserk on 3pt shooting is an aberration, not the norm. To create good flows, they don't move the ball as much as moving through picks. And they still set tons of illegal screens.
They don't have the length and the athleticism to dominate down low. KG played a great game taking it to Gasol but if he goes off again, he can be well contained by Bynum, whom he can't bump and dislodge at all. He still has great footwork, but lacks lifts so Bynum can easily recover and make his shots harder with that huge wingspan.
Rondo is not a great PG until he develops a good mid-range game. If his defender can stay 8 feet away from him when he has the ball at the top of the key, it takes away a lot of space in the middle, which is what a great half-court team needs.
And it becomes more obvious when the coach has to stress and preach the running game. In the finals when both teams learn and adapt through the many games they play, a slow, more organized offense is a lot more important and feared.
Of course, no matter how much Artest sucks on offense and stops the ball movement, his defense on Pierce is very important. PP is the only one on the Celtics team who has the driving capability, the long ball, and more importantly, the mid-range game.