Sounds more like documented cases of shooters that can't group with any pistol.
Ah the age old logic of "I haven't had any problems with my pistol, so any problems people are reporting must be them". I agree when I read "accuracy" complaints I become skeptical too. But there have been a lot of reports over on the S&W forums about this issue, again only with certain M&Ps. Many of these users try another M&P and find the problems go away. It got the point where APEX tactical was talking about fabricating their own locking blocks for M&Ps in 9mm to work on the issues. With that much behind it I begin to believe there might be some truth to it.