Hmm. Interesting if this decision was ultimately responsible for Twitter's declining traffic. Perhaps the same will happen to Linkedin? Of course even if it does we won't have evidence of causation, but it's something to keep in the back of our minds.
http://www.wired.com/2015/02/linkedin-api/
tl;dr: LinkedIn is pulling a Twitter.
I can't say I'm surprised. It's a common pattern: Step 1: plant a nice open garden that attracts lots of people. Step 2: put wall around garden.