From my understanding, this is a separate issue from bug #704231 in that bug #704231 is concerning Unity stealing Super combos from applications outside Compiz, while this issue is that Unity claims certain Super combos without making them available to Compiz. Mark Shuttleworth's first comment on the other issue was that Super should be reserved for window manager functions, which means it should be available to Compiz for reassignment.
Unity reserves certain key combos through standard Compiz means (e.g., Key to show launcher, Key to execute a command) but doesn't reserve others (e.g., Super-t to open the trash), instead opting to override the key. This means if a user tries to register Super-t in another Compiz plugin, Compiz doesn't complain like it normally does. This is bad, and separate from the issue raised in bug #704231.