Think of the force on the rider with the rope attached to the stern of the boat vs on a tower.
The stern the boat goes lower in the water with weight and on a tower the rope goes higher when on plane at wakeboard speed. The tower force provides an upward force versus a neutral or downward force when attached to the stern.
You can make a pylon yourself pretty cheap, check out www.diyTower.com
, or eBay. Try that or ride behind a boat with a tower to know the difference.