http://www.suite101.com/content/cooking-with-cast-iron-pots-a59702
Do a search on cast iron health benefits. Even the Lodge Manufacturing company agrees right before their paragraph on seasoning.
Seasoning coats the pan with carbon. I will agree that if the pan is rusty it will give off the iron but that makes for a crappy pan which the food sticks to. A properly seasoned pan will not rust and will give off iron nor will the food stick. It’s better then the crappy pans they sell as non stick.