The number of blogs hosted by microblogging site Tumblr just surpassed the number of “real” blogs hosted by venerable old-timer WordPress. Here’s what we can glean about the future of blogging and social networks like Twitter from Tumblr’s explosive growth. According to numbers dug up by Mashable, microblogging newcomer Tumblr has just surpassed the 20.7 million blogs hosted by WordPress–explosive