Some of the credit should go to swapping Trevor Ariza out for Ron Artest. Though the former has a solid defensive reputation, Basketball Prospectus' statistics show Artest holding opponents 8.8 percent below their usual production. By contrast, they were 7.3 percent better against Ariza.
The bigger factor, however, seems to be the Lakers' improved perimeter defense. All the trapping they did left them vulnerable to allowing open three-point looks on the weak side of the floor. Opponents attempted about a quarter of their shots against the Lakers from beyond the arc last year, the league's fourth-highest percentage. That rate is down to 21.2 percent this season, below the league average. The success rate on threes is down as well, from 34.9 percent to 30.0 percent, which is best in the NBA. By cutting down on their aggressiveness in trapping and doing a better job of rotating, the Lakers have made life very difficult for opposing offenses.
At the other end of the floor, the Lakers have not quite been themselves. Remarkably, their Offensive Rating is just 14th in the NBA. Part of that has to do with Gasol's injury. Without the Spaniard, the Lakers averaged just 107.1 points per 100 possessions. Since his return, that has leaped to 111.8. Still, that mark would put the Lakers eighth in the league over the course of the season, slightly below the Celtics.