Current Customer Not Allowed to Install Additional Boxes

We went to our local Cox store to get an additional DVR and 2 additional HD boxes. We were told we had to have someone come to our home to install them. And when asked why, we were NOT given a clear answer.

We currently have a DVR and 4 HD boxes. Adding the extra boxes does NOT take a technician. So to be charged to have this installed, never mind having to make an appointment is silly.

Please explain!