At first glance, Tumblr may seem just like Blogger or Wordpress: you write text in a box and it appears on the blog page. Yet, it has been crafted to enable a different kind of blogging - to enable curation of content. You can easily post pictures, movies, quotes and other forms with fewer steps than elsewhere.
Now, you no longer have to be a writer to be a blogger. You can just be a taste-maker, highlighting the content that interests you most. Whereas not everyone feels they are able to be a writer, everyone does have tastes.
As Google Trends shows, the results speak for themselves.
Top: Google searches for Tumblr vs Blogger vs WordPress. Bottom: The same for news references.