[rolling_stone]

Reportedly this plane had experience damage several years ago and speculation is that it was not checked or repaired properly, allowing the relatively small turbulence to cause the material to fail...in other words a normal plane would not suffer the same damage....

[Solson]

In general I would agree with that. But, detecting fatigue in carbon composites is generally difficult. If the cracks were too small to be seen with visual contact, they would have been missed. For a reference on non-destructive examiniation please look at this:

http://www.aviation-industry.com/atem/Acrobat/at53ndt.pdf