Is it possible the move is a CYA on the part of the studio? After all, they don't want to be accused of teaching people how to commit murder, so maybe they throw in deliberate misinformation precisely so their elaborate schemes wouldn't work in real life?
Sorta like in Real Genius -- the sciencey pranks pulled by Chris Knight and Ick, while they sound plausible to laymen, don't actually work and deliberately don't actually work 'cause the people making the movie knew they'd get a slew of imitators if the pranks were feasible. (You can't store frozen nitrogen in an off-the-rack refrigerator freezer, they aren't cold enough. And even if you could, a slice of frozen nitrogen shoved into a coffee machine wouldn't have the right weight/size ratio to get past the coffee machine's "slug detectors" ... just for instance.)
It's a thought, anyway.