I have a follow-up question relating to this question:
If amazon.com can bill without the CVV why does it ask for it the first time information is entered? Maybe they just silently discard it? Maybe the first transaction you ever do utilizes your CVV but subsequent ones don't?
I was looking at the specs for a particular payment gateway and one thought I had based on that was that maybe amazon.com could be doing a pre-auth for $0.00, with the CVV / CC#, getting a transaction ID for that and then passing the transaction ID to the payment gateway on all subsequent calls, charging a different amount each time?