I'm sorry, I really don't mean to be rude, but I've got to agree with the other fellow. Yes, he came off a little snippy, but your counterattack is even more pedantic and confrontational.
Your list of people who misuse "beg the question" starts with the British Parliament and continues through the US Congress and the US House of Representatives. These are people who, in general, fit the description "pompous gas bags," people who use words to manipulate and mislead, with little regard for proper usage. That the NYT, the TLS, and the Guardian are on there is a little distressing, but I'm sure there are factions within those groups who still hold out for the proper meaning of the phrase.
Moreover, the rules should be a little stricter, perhaps a bit more conservative, for writing than for spoken words. Writing gives you the chance to stop and think, and to revise, so it's not unreasonable that the standards should be a little higher. It should resist casual change, if only because it lasts longer. So the "language evolves" argument (which sidesteps the realization that evolution often leads to dead ends), doesn't hold so well there.
Besides, most people don't even say "beg the question"; more than once, when I've used it in casual conversation, I have had to explain it to someone, so it's not like a split infinitive (which was never wrong, anyhow) or a who/whom confusion. To claim popular support for the phrase is to beg the question, "what constitutes colloquial usage?"
So in short, yes, it's bad to get uptight about the wrong usage; but it's even worse to get uptight about the right usage.