From what I've gathered, Twitter would be upset that LinkedIn doesn't support "expanded Tweets" (so you can preview images and links), among other features. If the features make the experience nicer, then wouldn't that be one more reason to follow the link to twitter.com? Having the full feature set on LinkedIn would decrease Twitter's traffic. Not to mention that they're asking LinkedIn to make their interface more complex, which LinkedIn is right to reject.
"You need to be able to see expanded Tweets and other features that make Twitter more engaging and easier to use."
"You need to be able to see expanded Tweets and other features that make Twitter more engaging and easier to use."
-Michael Sippey, Consumer Product Lead, Twitter
https://dev.twitter.com/blog/delivering-consistent-twitter-e...
http://tech.fortune.cnn.com/2012/07/06/linkedin/