From the desription you have mentioned, it looks like a polarizer that was being use for Analog systems. There used to be a fixed LNB in one orientation (either Horizontal or Vertical) and the polarizer was used for switching to the other orientation. This was being done automatically by the receiver. Whenever a channel is changed, the receiver sends a series of pulses for the motor to rotate the polarizer to the correct position that is set in the channel settings. In order to feed these pulses, a seperate cable had to be run from the receiver to the polarizer and carried the three cores - as you have mentioned - 0V, +12V (not 5V) and pulses. The other option was to use two LNBs placed in opposite orientation, in which case no polariser was needed.
In Digital reception, the present lnbs (universal and C-Band, that I know of) receives a voltage signal (14V) from the receiver for swithcing the orientation (H/V). This voltage is fed through the same cable that carries the signal. The whole process is automatically taken care by the receiver and no intervention is needed by the user.
Hope I have understood your question correctly and hope you are satisfied with this answer.