It's a dicey business to reveal the secrets of the brotherhood to the laity; look at what happened to Edward Snowden. But I step forward today to tell you that the people you would imagine to be most knowledgeable about English grammar and usage, English teachers and editors, are often ill-informed and sometimes startlingly ignorant of basics. 
At The Economist, Robert Lane Greene has already exposed that English teachers, competent to distinguish between it's and its, are at sea on syntax because English departments have largely abandoned the study of grammar for the analysis of literature. (I urge you to click on that link and read the whole article.) The study of grammar is left to linguists, who have developed their own vocabulary for the discipline and speak mainly to one another rather than to the public. 
What holds for English teachers is true a fortiori for journalists, some of whom can get a degree in the subject without even taking the rudimentary instruction in grammar to be found in an editing class. 
Those of us in the older but not yet passing away generation had the traditional schoolroom instruction, which, in a summary by Hentry Hitchings that I can never resist quoting, was compounded of "bogus rules, superstitions, half-baked logic, groaningly unhelpful lists, baffling abstract statements, false classifications, contemptuous insiderism and educational malfeasance." Younger editors have not even had the benefit of that 
At the lengthy exchanges in the over/more than brouhaha at LinkedIn, which provide enough codswallop to supply you into the next decade,* my esteemed colleague Ruth Thaler-Carter describes how journalism has operated:
"How 'over' and 'more than' are used from now on in work that follows AP may depend on how writers learned their meanings and a distinction between them. That distinction is the first thing I consciously learned about AP style way back when I was a reporter for a family-owned weekly newspaper in St. Louis that had no style guide at all (I don't think anyone there even knew what AP was. I was usually the only one who had any previous journalism experience or training, and that was mostly from college.) We were joined briefly by a reporter who had worked at the Rocky Mountain News and told me about over/more than, and it stuck in my mind ever since."
Reporters and editors, lacking formal instruction in grammar and usage, pick it up through the lore, the "somebody told me once" method. And it works. When I tried out at The New York Times, the slotman, Dean Gladfelter, instructed me as he went over my copy that conclave means a secret or closed meeting, after its etymology, com + clavis, "with key," and that detail has stuck in my head for twenty-eight years. 
Unfortunately, those authoritative statements by journalism instructors, editors, and copy desk chiefs will stick just as firmly when they are misinformed.
With no formal training in grammar and usage to rely upon,** and with an apparent disinclination to look things up, journalists cling to the little set of shibboleths they have been given, the flotsam that keeps them afloat in the language. What we see then is comical outrage and defiant resistance when someone explodes some spurious rule. 
As Dr. Johnson observed, "We are more pained by ignorance than delighted by instruction." 
*Rather than address any of the substantive points exploding the sham rule--the evidence of its arbitrary origin, common usage for centuries, dictionary entries, and the arguments of prescriptivists like Theodore Bernstein and Bryan Garner--its defenders resort to ever more fanciful elaborations. One of the latest at LinkedIn is an argument that what its proponent says is the usage in Romance languages should also apply to English. 
**There is a book, Grammar for Journalists, yellowing copies of which can still be found in newsrooms. I had a look at it for the first time yesterday. (I was an English major, and therefore a snob.) Forty years old, it retails the conventional schoolroom grammar. But even it points out that over and more than are equivalent in the dictionary, though not in the AP Stylebook

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