Actually true. Cast iron shouldn't ever have soap applied. Wipe with some oil and re-use! It's almost all we use (that and surgical stainless steel, but that sticks pretty bad when a "non-stick" type pan is needed). Dishwashers are for forks and wine glasses. Right?
I have an iron skillet which was a gift 20~ years ago. Except for the initial, pre seasoning scrubbing, it's never had soap or detergent on it.