Thanks for the upvote. You need to give them the memo key - your memo key - to show that you have control of your account. That's important for security.
It also acts as a check against (say) you making a typo when you enter your registered account name.
Ok, I trust you on this even if I don't see the same type of security for BTC or BTS withdraw. Still looks strange to me...
Yeah, it is a little strange but well-intended.