Interesting. There must be some internal inconsistencies across accounts (not surprising for something that's existed this long). So maybe they are slowly working through the changes as they hint.
For instance, in the past month I received this notice, unprompted, from amazon:
Greetings from Amazon Web Services,
In the past, you have used the same email address and password to sign in to Amazon.com and AWS. In response to customer feedback, AWS is updating your account to make your access to Amazon.com and AWS independent. You can continue using this email address and your current password to sign in to Amazon.com. However, the next time that you sign in to AWS, you will be prompted to create a new password and will have the option to register a new multi-factor authentication (MFA) device. MFA is a best practice that adds an extra layer of protection on top of your email and password.
For instance, in the past month I received this notice, unprompted, from amazon:
Greetings from Amazon Web Services,
In the past, you have used the same email address and password to sign in to Amazon.com and AWS. In response to customer feedback, AWS is updating your account to make your access to Amazon.com and AWS independent. You can continue using this email address and your current password to sign in to Amazon.com. However, the next time that you sign in to AWS, you will be prompted to create a new password and will have the option to register a new multi-factor authentication (MFA) device. MFA is a best practice that adds an extra layer of protection on top of your email and password.