The over-reaction seems to be centred on the fact that it happened in London so it was easy for the journalists to reach and that social media allowed images and ideas to be spread quickly mushrooming the impact that people were feeling. If 24 hour, Internet home pages facebook updates and tweets are all telling you about the riots they seem disproportionately worse. It also allowed it to spread worldwide quickly.
Remember the 20 days of rioting in Paris in 2005 from October 27th to November 15th. Thought not!