I think you're over-estimating Amazon's intelligence there. I recently had an order confirmation email from Amazon for something I hadn't ordered, but I noticed that it had been sent to one of my other email addresses (as had lots of "Welcome to Amazon"-type emails), so I assumed that someone had just made a typo with their email address setting up their new amazon account, as Amazon stupidly don't send you an 'activation' email when you set up a new account or register a new email address. So I contacted Amazon CS to tell them someone had accidentally set up a new account with my email address, and they said they'd contact the account holder to rectify the situation.
Can you see where this is going?
Within 5 minutes, I received an email from Amazon advising me that I'd used an email address to set up my new account that belonged to someone else, would I mind changing it?
When I called up Amazon again, the CS rep told me not to worry as even though I'd received the email, the Amazon account holder would have received it too as we both shared the same email address. 8-(
In the end I just did a "forgotten password" reset on his/her account (as authentication is by email) so they wouldn't be able to access the account any more, and ignored the subsequent password reset links I received when they tried to log-in a few days later. I had been tempted to place an order through the account for something personalised with the message "Get your bloody email address right you f***wit" but I guess that would technically have been theft so I never did.