While I must admit that some of the sentences I've read about do seem a little over-zealous, I also temper that sentiment with the fact that the UK judicial system has been notoriously lenient on some types of offences in the past couple decades and these riots are in a small part the culmination of that. A demographic, marginalized and widely accepting petty crime as a lifestyle, has learned over 20 or so years that the judicial system is inclined to do very little about their actions. They expanded this to a belief about policing, and were partially vindicated by the sheer amount of time it took for the authorities to get a grip on the issue. Now they have the audacity to whine about the judicial system actually taking their crimes seriously?
Then again, I was a proponent of invoking the old riot act and calling the military out to the street corners at night to deal with the rioting, so perhaps I lean a little toward the punishment/deterrence side of the justice scale anyway.