What is the minimum separation between two landing A380s?
In general, the heavier an aircraft is, the greater the wake it produces but, it is also less affected by the wake of other aircraft.  In particular, an aircraft can always resist the wake turbulence of a lighter category aircraft.

It was found that the A380 was not affected by wake turbulence from any aircraft in front, including another A380, down to the minimum RADAR separation used on approaches which is 3NM.

The RADAR separation used on any particular approach might be greater, but not less than this minimum therefore, there is no need to apply wake turbulence separation to a following A380 and the required RADAR separation for the approach is applied.