You describe the 18-month renewal of implied consent. What if it worked in reverse? If there was a pre-existing business relationship, consumers could click and say they didn't want to receive information any more. It might come two years afterwards, but when the communication came, the consumer would simply say, “Okay, no more. I'm done considering your offers.” I'm wondering if the consumer, from your perspective, would favour one over the other.
On September 30th, 2009. See this statement in context.