Just to illustrate what a morass "poor grammar" is, I have, wearing my ex-professional proofreader hat, gone through the article to highlight the areas where I could find fault with the article for incorrect usage.
People Who Use Poor Grammar should be: People Who Use Grammar Poorly.
I have a "zero tolerance approach" should be: I have a zero-tolerance approach.
people who mix up their itses should be: people who mix up its and it's.
passed over for a job — even if should be: passed over for a job—even if.
I don't point this out to be pedantic or to level at the author a tu quoque, but to point out that the idea of an "English grammar" that you can apply universally to writing is a myth. At best you can create a style guide, or follow an existing one. Expecting employees to be able to follow a known style guide is a reasonable request. Expecting them to score perfectly on a grammar test against a style guide they've never seen, without (presumably) computer assistance, when scored by someone who believes that they're capable of scoring a grammar test without recourse to existing style guides, is foolish, in exactly the same way that expecting a programmer to remember whether String.find take (needle, haystack) or (haystack, needle) as its arguments is a terrible interview technique.
All the examples you cite are stylistic choices and have nothing to do with "grammar". (I also personally disagree with all your suggested edits, especially the first.) Using Hungarian notation in C may be poor style, but it conforms to the C grammar.
For clarity, when I talk about "grammar" here I'm talking about what Wikipedia calls "orthography", which is what I think the OP was talking about. You're right that #1 is a style correction and #3 is a typographic correction--on the other hand #2 is unambiguously orthogaphic[0], even if it's not as well known as it's/its, and if the writer feels justified in making up "itses" to mean "it's and its", presumably because people can infer what it means from context, that puts them in a very shaky position as a prescriptivist.
The interesting point that I'm trying to make isn't that that author is wrong or right, because I don't really care much about slips in orthography. It's that once you take a prescriptivist stance you're either making an appeal to popularity or you're entering an arse-kicking contest with a seven-legged monster with no arse.
> once you take a prescriptivist stance you're either making an appeal to popularity or you're entering an arse-kicking contest with a seven-legged monster with no arse.
That's an extreme and unjustified dichotomy. The article is written in an informal linguistic register, not in the voice of a 19th century naturalist writing for the Royal Society. (Is my use of the passive voice in the previous sentence also "incorrect" because style guides frown upon it?)
Still, the article's language is clear, precise, and suggests that the author takes pains to accurately communicate his thoughts. We haven't seen the author's grammar test. I would suspect that it tests the kind of linguistic economy I'm talking about, not whether the test-taker has memorized obscure passages from Strunk and White. As such, the test is probably effective at eliminating candidates who don't give a damn about correctness.
I have a "zero tolerance approach" should be: I have a "zero tolerance" approach.
your third edit, which I also don't agree with, isn't quite right, it should be: people who mix up "its" and "it's".
fourth edit: I've always hated this jamming of words together with an em-dash: it appears that "job" and "even" have something to do with each other, but they don't.
Oh, wow, someone nitpicking this guy's grammar — never saw that coming. What an unhelpful, predictable comment.
FWIW, I don't believe the author was talking about style guides at all anyway. Rather, he seems to be discussing general and very basic principles of English.
Very basic in whose judgement? If it's the author's (and presumably yours), fine, but then it's not a business case, it's a shibboleth. If you're agreeing with the author's claim that there is a "silent majority" (which I always find a dubious argument) of people who have their confidence in your business impacted, then you're far better off investing in a process that catches these errors--many of which can be caused by typos, rather than ignorance--before they are seen, rather than relying on an up-front test that's never retaken.
Someone else on this thread made an analogy to push-ups. If, as a business owner, you feel that it's essential for your business that any employee can perform 20 push-ups at any time, is it better to test them before they begin employment, or to put them on a brief training course when they join and have regular check-ups on their ability?
I actually don't agree with the author, so I'm not going to defend him. However, I don't disagree with the author based on the fact that he made some completely understandable mistakes in his own post.
People Who Use Poor Grammar should be: People Who Use Grammar Poorly.
I have a "zero tolerance approach" should be: I have a zero-tolerance approach.
people who mix up their itses should be: people who mix up its and it's.
passed over for a job — even if should be: passed over for a job—even if.
I don't point this out to be pedantic or to level at the author a tu quoque, but to point out that the idea of an "English grammar" that you can apply universally to writing is a myth. At best you can create a style guide, or follow an existing one. Expecting employees to be able to follow a known style guide is a reasonable request. Expecting them to score perfectly on a grammar test against a style guide they've never seen, without (presumably) computer assistance, when scored by someone who believes that they're capable of scoring a grammar test without recourse to existing style guides, is foolish, in exactly the same way that expecting a programmer to remember whether String.find take (needle, haystack) or (haystack, needle) as its arguments is a terrible interview technique.