Video monitoring is harder to do, as it requires the installation of a specific video camera and monitoring equipment, as well as a specific set of people to monitor a particular user or group of people. This is typically done in public places (elevators, locker rooms, and the like) but can also be done secretly in an office or cubicle.

Here's a link to a press report on a recent court case regarding video monitoring that might shed some light on why video monitoring in the workplace is a difficult issue to discuss without the specific context of the problem at hand.