You cant call the army in, they generally arnt trained to handle these sort of situations and it also inflames the situation as it turns into a military action against your own people.
The police should be getting tough though, this idea that the police comissioner is saying 'parents get a grip on your children' and then having burning buildings all over the news basically making it look like the police cant handle a bunch of kids....its not a good look especially with the olympics next year.
Is it a sign of things to come? I reckon it is, Greek riots, UK riots.....I think there will be more before the Olympics begin next year, not sure where though