If I wander back to the topic, I would guess that a wad of conductive material stuffed into the inside of a chicken would certainly do two things:
1) Promote heat transfer
metals all promote heat transfer and, with the liquid heat sink inside, will heat and transfer the air temperature better than just air alone. Particularly if the can is in direct line to the heat.
2) Provide a repository for "schtuff"
Herbs, spices, beer (a waste in my opinion), or other items, the can provides a receptacle into which the cook can shovel differing items to flavor the end product.
I'm not a b/c chicken guy because a well rubbed, butterflied chicken that has been brined is my taste. Note, my taste -- not everyone's. But there should be some Alton Brown geeks out there that would know the science behind a beer-can chicken. Or maybe we ougta ask AB himself?