If we're going to start arresting people for internet insults and empty threats then the police stations are going to be very very busy.
I don't think everyone is going to get arrested for "internet insults and empty threats", the point is that they want to be seen to be doing something on high profile cases.
Remember some Welsh student got banged up for having a pop at Muamba on Twitter not that long ago, similar thing.
Same goes for the people 'inciting riots' on facebook last year, it was a very high profile news story, the authorities come down hard on somebody to make them a scapegoat.
Regardless of whether one agrees with this approach or not, I don't think it is indicative of a wholesale widespread change in policy. If I abuse somebody and say I'm coming round to smash their face in on a social networking site, and it is seen by a handful of associates, nothing will happen. If I do the same to a celebrity in such a fashion that it gets instant exposure to tens or hundreds of thousands of people, or in relation to a high-profile event and it gets mainstream publicity, then I'm at risk.