Ok, Here are a couple of useless Theorys
Because the smart is so narrow the smart is hitting those nails left in the road by the last contruction boom that no other car had been near in the past 5 years
Or,
because the Tires are so narrow instead of having a harmless center puncture that can be repaired, its more likely to get a sidewall puncture than most cars - Its a deal between Benz and Conti to sell more tires
Or,
Since the wheel base is so short when the front tire tosses it to the rear they are realy much better at playing catch than most cars.
And maybe the real Tin foil hat guy would say that smart knew their was a problem with this, and held off bringing the smart to the US untill the construction market was in the tank so the issue would not come to light untill years later