This story has an underlying theme shared by another story here on HN a few days ago about a mobile app that reached a million users in a year without any viral

This story has an underlying theme shared by another story here on HN a few days ago about a mobile app that reached a million users in a year without any viral marketing (http://news.ycombinator.com/item?id=4205571 http://news.ycombinator.com/item?id=4205571). And that underlying similarity is this - a relentless focus on customers can make up for low marketing spend.