I've never seen a horse that needed their poll padded because of the weight of the bit! I'm kind of shocked that the rider would continue to use a bit that did that to a horse. I wonder what the point is? Simply liking the silver on the shanks? What could the benefit be?
Do the guys you mention address that? I'm kind of a fly by internet user and am curious about it now.
(stole image from cowchick)
If you add weight below the mouthpiece, the bit will tilt closer to vertical when suspended from the mouthpiece like this (and while it's held by the horse), and it will apply more pressure to the horse via the spade when it is anything other than vertical.