The relationship between WordPress and Tumblr has always been pretty friendly: Tumblr's own blog used to be on WP, WordPress.com supports Tumblr as a Publicize option alongside Twitter and Facebook, our Akismet team sends them daily emails of splogs on the service, and there's healthy import and export traffic both ways.
Now an audience of more than 1 billion people is only a click away from every voice online, and remarkable stories and content can gain flash audiences as people share via social networks, blogs and e-mail. This radically equalizes the power relationship between, say, a blogger and a multibillion dollar corporation.