Windshield problems of the 2004 Mercedes Benz C Class

I was traveling on the freeway (approximate speed 60 mph) when I heard something hit the windshield of my 2004 mercedes c240. There was no immediate signs of damage. However, about 30 minutes later after I had made stop and later returned to the car I noticed a 12 inch crack in the windshield. I believe there is a serious design defect with the windshields in mercedes. A CO-worker of mine has had to replace the windshield in her 2004 c320 mercedes twice within the past 18 months. The service reps have told her that this happens on the time, especially for commuters who travel the 91 freeway here in southern California. I would think that r&d would have done sufficient testing to ensure that a windshield could withstand contact with a rock or pebble.