Thanks for asking an important question. If the antenna system ground is not bonded to the electrical service ground, I believe you can significantly improve your antenna grounding system.
As I point out in post #20 of the thread,
http://forum.tvfool.com/showthread.php?t=901, I believe the NEC is correct to require that the coax and mast be connected to the existing electrical system ground... And I prefer to treat each as separate connections until they meet at the electrical service ground.