Correct.
You can never change any address that sends e-mails to you.
Some forum software allows to change your e-mail address so you can receive those messages on a new address, but since you can't change your address here, this isn't possible with this software.
This isn't a choice by the Arduino team, it's a choice by the forum software developers.
They decided that your identity is defined by your e-mail address, so changing addresses would be like becoming a new entity.
Something for SMF, those developers, to change as soon as possible because calling that retarded would be too gentle to them, and insulting to some other people.