Actually, I am stuck with "2 million blog posts daily" stuff. There were no references so I searched over the internet and found that "2 million" belongs to wordpress.com network (including subdomains and jetpack blogs) [1]. It seems that every other article/infographic also uses this number but it is obviously inaccurate. There are many other blogging media (medium, blogspot, other self-hosted software). And also there is tumblr (it is up to to accept it as a blog service).

[1] https://wordpress.com/activity/posting/