Both of those two above cases involve tracking people both in public and in private. Furthermore the former involved compelling a company to fork over private information.

Traffic cameras, by comparison, only record people's in public. A police officer isn't violating privacy laws by standing at an intersection and writing down the plates of cars passing by is he? Flock is just automating that task.

The whole reason why we have license plates is to facilitate monitoring cars. If we really think that people have a right to keep their vehicular activities private, then surely the bigger privacy violation is the fact that we require cars to display unique identifiers in a prominent manner?