Why is it so bad really though? Havent seen them yet.
There are two basic reasons: rebounding and rotations.
The Spurs have been one of the top defensive rebounding teams for the past decade. They generally have limited teams to an one & done offense. And they force teams to use the majority of the shot clock running their offense to even get off a halfway decent shot (the boring play that the common fan sees). They take away the offense's comfort zones and make them work for their points. This year they are getting killed on the glass...they are weaker than normal on the offensive boards. And teams are pounding their offensive glass with great success...for example, at the end of regulation last night the Wolves had outscored the Spurs 23-0 on second chance points.
The second area of concern is defensive rotations. The whole team...both young and old...seems to be having communication problems and mental lapses. They seem to hestitate that split second before rotating. Or two players follow the same cutter leaving another player open. Teams are getting more uncontested shots than I have seen for a Spurs opponent in a long time. There are some reasons (excuses?) for this. The new guys (Mason, Hill) are still learning the defense. Injuries has forced Pop to give older vets (Thomas, Finley) more minutes than he would otherwise.
Also contributing to the overall record is Pop's tendency to use November & December as experimental months. He will play different combinations on the floor. He uses a deeper bench to see who can produce and who needs more practice time. He will let the team play through different situations ala Phil to see how they react. Pop will use these early season games as teaching tools.
Also the opening schedule wasn't kind. The Suns were motivated to come in and beat the nemisis that knocked them out of the playoffs again. Shaq wanted to prove that he wasn't washed up and as a whole they needed to show that they were contenders in a new system. The Blazers were playing their home opener and were trying to show they belong in playoff discussions. That game could have gone the other way if Finley's 7 footer hadn't skimmed off the rim. The Mavs are the Spurs biggest divisional/state rival and needed to prove they are still relevant in the west as well as that their new system works.
Especially with the Mavs one should look at the boxscore. The Spurs had 11 players with 12 or more minutes and even the 12th player (vaughan) played over 10. This is more like a preseason boxscore than a regular season one.
Duncan was the only player over 30 minutes....Mason played right at 30, Parker 29.5 minutes. The Mavs had 4 of their starters play 35+ minutes. And their top 2 reserves played 18+ minutes. In a blowout win their 3 end of the bench guys played 2 minutes each. Does anyone really believe come the real season that the Spurs will go that deep in their bench?