I think the %s are that high as long as everyone buys into a good defensive philosophy, like Boston. Pierce, Allen and KG don't win a thing without that defense.
I would think defense would be a given with this roster.
Assuming Brand is fully recovered, he will be a great defensive presence next to Sam. He boards, blocks and is quick enough to use for traps.
I also expect Iguodala and Young to be one of the best defensive swing combos in the NBA.
Miller will always have problems against amall/quick PG's, but he will have a great amount of help.
It would be great to keep Evans, but I expect Smith and Speights to be decent defenders with time, and Carney could become a high level defender.