Stack Overflow and Github's primary audience is developers. Reddit's started out with a mostly developer audience and still today has a huge crossover. It absol

Stack Overflow and Github's primary audience is developers. Reddit's started out with a mostly developer audience and still today has a huge crossover. It absolutely makes sense to support mark down if your audience is developers. I don't find gmail to be an exception to the rule at all - all the big webmail providers offer full WYSIWYG support.