(That was a genius move of Profile Books, btw: to publish both the Punctuation Panic book, and its Refutation.)
As Crystal argues compellingly, Internet and SMS discourse don’t make people forget the rules of formal punctuation they have been taught in school (sometimes, successfully). As Zeibura S. Kathau puts it (What does your English accent sound like?): “I can speak Job Interview too.”
But it does allow them to ignore those rules in certain registers, which are more relaxed about the rules of formal grammar, and where you need not punctuate in Job Interview. That does not mean there are no rules at all in that register; ending an exchange with a period in an text means something distinct, in a register where the default is to leave it out. Not to mention the use of periods to represent. emphatic. speech. like. this.
And if you can command two registers of grammar and punctuation, rather than one, why, surely you’re better off.
Now, Quora tends to the formal rather than the informal side of punctuation: Wikipedia rather than Twitter. And yes, some contributors are slack about it, because they treat Quora as an extension of their Twitter or texting register. We speak a toned down version of Job Interview here, and some don’t tweak to that immediately. That does not necessarily mean those posters can’t speak Job Interview.