"Jack, Grammarians usually ARE educated writers. Did you think they came from some strange planet just to upset lazy ignoramuses?"

Yes, pretty much actually. But to the difference: the educated writers who are referenced in descriptive grammar analyses don't include grammarians themselves. Descriptive comparisons would lose all meaning if grammarians were included as examples, since it is the grammarians directives that are being assessed. But I think you already knew why grammarians, who are merely writers about writing, would be excluded, right? What I find most amusing in descriptive references are the numerous examples of grammarians contradicting their own rules, often applying the usage in the very same assertion in which they are condemning it!

I've been a proofreader for 25 years and counting. The surest way to cure Stefan of this nonsense is for him to become one too. Having a job monitoring the grammar of business reports, dockets, annual reports, etc. will teach him that 1) correcting grammar is a bloody bore, which in turn will make him realize that 2) a sign in a store or elsewhere is the least of his troubles, and 3)the prescriptive grammar he is valiantly defending is for the most part arbitrary, disagreed upon, and stilted. For instance, if he were to peruse a copy of Merriam Webster's Dictionary of English Usage, which adheres to a descriptive, comparative analysis of English usage, he would find, much to his confusion, that the self-appointed grammarians of yore who concocted most of the prescriptions and proscriptions we learned in school were simply making it all up to suit themselves. Proper grammar is defined by the common usage of educated writers, not what grammarians have tried to enforce. Grammarians have been at odds with and ignored by those educated writers (and everyone else) for centuries. No one is interested in defending the grammar of the past, only the present, familiar grammar of today. What does that tell you?