It's not making any sense. I've read somewhere that Aeria doesn't want us to register at EA's website, but we can't seem to do it from their's. I'd like to know what's going on.

Look at the stickied thread:
Using AP in Need for Speed World
http://www.aeriagames.com/forums/en/viewtopic.php?t=1429181

It shows the screen you are trying to get to in order to create a new account with EA that uses the same email address as your Aeria one so you can use your AP in NFS World.

The key is that if you already have an EA account with the SAME email address as your Aeria account THEN you MUST go to EA's website and CHANGE the email address of the EXISTING EA account to something else, DELETE your browser history/cache, THEN use the Aeria website's play now button to get to the special EA account registration page and use it to create a NEW EA account with the same email address/password as your Aeria one.

Clear as mud? Good luck!

and if you have played need for speed world before, this link will help you as well.
http://www.aeriagames.com/forums/en/viewtopic.php?t=1429315