From the article:
Perhaps Tumblr wants to remain a niche platform, mainly designed for spreading memes among a core set of urban users
While still new to Tumblr (I’ll celebrate 2 months only in a couple of days), what I think I’m seeing in Tumblr is more like a photo and music bookmarking service.
Tumblr has a couple of interesting features to help memes grow up pretty fast, but this doesn’t seem to be the case. If you check the popular section you’ll notice that there are only photos and a couple of songs in there, but no text.