PersoLatin, you make a valid point about what has been termed Faarsi e Shekaste (فارسیِ شکسته) being in effect the high point of informality and the overshadowing feature in all colloquial utterances. This chipped and chiseled Persian is being used all over the media for spoken and written communication as if it were standard, and yet the more it feels like a compelling force, the more it is perceived as exhibiting less authority. میشوند and دارند are somehow well established and are not "getting old" and dying out, not just yet. But to go back, our grammar books do continue to pronounce the construction in question colloquial, perhaps because, unlike خواستن, there is no logic in using داشتن as an auxiliary in the construction of the continuous tenses. I don't know about a possible etymological reason, but the present meaning of the verb certainly doesn't justify its use, whereas with خواستن, the notion of intention and future action is already hidden in the meaning. Still, and this is just a personal feeling, داشتن to signal continuous action will not sound so jarring in any context or register, if only because there isn't any other verb in the lexicon that can better serve the purpose. All our verbs, as far as I can see, are equally inadequate, and داشتن just got there first.
