I and a friend also applied to Robotics, Systems and Control and our "withdraw" buttons are also gone, same as in everyone's case. I wouldn't ascribe too much meaning to it, honestly, as it's probably just a quirk/bug of their system. My Computer Science application (which was already accepted last week) still has the button, though.
Judging by last year's gradcafe listings, the RSC replies (both positive and negative) start coming in throughout the first week of March. So still a tiny bit of waiting left to do, I guess.
On another note, anyone accepted for the CS MSc, Theoretical Computer Science track? Do you know if the ETH does waitlists at all?