Twitter blocks Tumblr's "find friends" access too

Marco Arment on Twitter's blocking of Tumblr "find friends" access

Twitter will now only permit large services to add value to Twitter, not get any value from it. 

So when Twitter says something like “[developers] will need to work with us” to “identify areas of value” when they get big enough for Twitter to notice, I don’t have high hopes for what “working with us” might actually entail. 

Twitter clearly see themselves in a strong enough position to be safe from being disrupted. It's certainly hard to argue against it.