Lurker,
I wasn't trying to say that the Spurs didn't have a top defense -- only that lowest point totals for opponents isn't the best way to determine who has the best defense in the league.
Personally, I still feel like fg% is the best determination -- but, along with point differential, it too has it's drawbacks. I think a combination of the two gives the best perspective -- while I think the lowest points per game isn't something to really be considered.
The Spurs run a lot more than they used to but they still don't run as much as the Mavs -- the Spurs bread and butter is the halfcourt -- I think the Mavs would prefer to run but can operate in the halfcourt as well (which was a key in helping them get the "monkey" off their back last year in the playoffs).
As for Pop's limiting minutes to his rotation -- look at the age of his players: (none of these players have had a b-day in '07 yet)
Horry is 36
Barry is 35
Bowen is 35
Finley is 33
Fabs is 31
Duncan is 30
Manu is 29
Parker is 24
With the exception of Parker, the Spurs team is aging and you don't want to use their energy up in the regular season (the Lakers did that one year with Horry and he was shot for the playoffs).