Quoted from BoJo:Not all wood had the same hardness and I wouldn't put it past Stern to have switched to a lesser wood if it means saving a few bucks. They are all about cost cutting so wouldn't be surprised if they switch to balsa wood in the future.
If your referring to recent Sterns versus all JJP games then the answer is YES....several tests have been done to confirm hardness of the Stern play fields are inferior