As i mentionned in an other post about it, Twitter seems not respecting API neutrality (same paradigm as Internet neutrality), the fact that all API 3rd-party users may have the same rights, access and limits to your API, if they satisfy same primary conditions (free or paying users)
Instagram, Linkedin, Tumblr...who's next?
They have gone crazy since they want to have their "consistent user experience"...
Do they fear that people can take their social graph to Tumblr? I never thought Tumblr was anyway similar to Twitter. Tumblr is altogether different beast when compared to any other social platforms.