Since NYPD is involved, I tend to agree with you. Were TSA on the case, grannie would best leave her knitting bag home.
However, there's only so much a 40,000 strong police force can do to to thwart these scenarios from unfolding.
In 1997 an Islamic terror cell in my borough was planning on blowing up the Union St. subway station.
The only thing that prevented them from doing so is that one of the original participants got cold feet, and ratted out his accomplices.
Sometimes the only thing you have to rely upon is luck.