Agreed. Where cops are required to wear surveillance gear, they are on their best behavior, because the video is available in court--this has already been demonstrated in the EU. And that's not up to the chief of police. Your lawyer can demand it. And Google glass feeds to the Google servers, not the police station. Ultimately, the cops don't own it, so they can't just delete or edit what they don't like, they can only modify their copy, which is not the master, which your lawyer can request. So they will be very careful to make sure that nothing incriminating appears in the feeds.
This is surveillance of the cops as well as citizens--souveillance, not just surveillance. Read Contrary Brin to find out what souveilance is. All the conspiracy theorist here need to take their tin foil hats off for a moment and try to understand what this really means.