Just because they are riot police doesn't make whatever they are policing a riot. Quite often you seem to see lots of police got up in full riot gear (and not showing their ID numbers, apart from anything) to police apparently completely legal and peacful protests.
I've always thought if you gave someone the equipment, they are more likely to use it. If you put someone in body armour and give them a riot baton, they're subconsciously conditioned to the fact that they may come under physical threat and will probably react in a more aggressive manner to perceived provocation.
I'm also firmly of the belief that the public react more positively to policeman in standard uniform than someone who looks like they've come prepared for war.
That and the fact that The Met's policy to protest seems to have hardened over the last few years. There seems to be much more 'overt control' going on and stuff like kettling and the like never used to happen.
Jon