There is nothing new or special about the Twitter rulings in the UK. Whether you agree with it or not, if you wrote similar messages to someone via letter 20 years ago you could get in trouble. Simply changing the medium hasn't changed the legal ramifications.
Aside from the fact that there have been actual changes to the law (mentioned in my "vague ideas" clause), what's changed is that people used to post obscene and threatening things on usenet, and whenever the police were involved, nothing ever came of it. With Twitter in the UK, in 2014, people now go to prison for posting such things.
Of course Twitter is more popular than Usenet ever was, but I'm not sure whether that's more the point than a gradual erosion of freedom of speech in the UK which I personally think we've seen.
