Nope, like all other large providers (Facebook, Google, etc.) Amazon allows users to use e-mail addresses to log in, but they are not canonical stores of identity. In fact, Amazon is the most humorous example you could have pulled, because Amazon actually allows multiple accounts with the same e-mail address, and uses the password to differentiate (which is pretty much what jointb86 said, but I doubt if you knew this is the case that his comment was clear).

"Why Does Amazon.com Allow Multiple Accounts With the Same Email Address?"

http://www.experimentgarden.com/2009/11/why-does-amazoncom-a...

"Note: If you change the e-mail address on your account to an e-mail address that is already associated with another Amazon account, we will ask that you first verify your e-mail address."

-- http://www.amazon.com/gp/help/customer/display.html/?nodeId=...