That's a good question. They have the best defense (statistically) in the NBA. And it's by a healthy amount. They also have an average to good offense (LA, by comparison, has a solid D and an average to good O, so Philly is superior to them). They have a strong record so far, and they also have a very interesting history of blowouts. And honestly, this could be a huge reason:
Wins by 10-19: 11
Wins by 20-29: 8
Wins by 30+: 4
So, 23 of their wins are by double digits.
By comparison, LA's breakdown:
Wins by 10-19: 6
Wins by 20-29: 1
Wins by 30+: 1
So, 8 of our wins are by double digits.
The ability to blowout teams is positively related to a team's success. I think that if LA did a better job of keeping those big leads they often build up, they'd be in much better shape (both in terms of my measures and in terms of their records). For instance, I was watching last game with my daughter. She looked up and saw the Lakers were losing in the first half. She said, "I thought they build big leads early and then lose them." If someone who like never watches games knows that about LA, it's a symptom of a problem.