You actually need a valid email address linked to your Bitcointalk account for security reasons tomorrow.
It's not a must and a valid email can become invalid or useless if that email provider service was bankrupted and closed their service.
Yes, you are absolutely right, and in such scenario, that's a more reason why it's also good for people wanting to register an amount on this forum to use a reputable email hosting provider such as Google or Yahoo mail (i.e for people living in areas where access to Google or Yahoo isn't prohibited).
How theymos investigated a possible hacked VIP account can help you understand it more.
VIP Member hacked?Thanks for sharing the link to this, regarding Theymos investigation, because I actually learnt a lot from the thread regarding forum account security.