On the 2006 ACAP of the A380 the OEW of the Pax-version is given with ~270t, and the freighter is given with 250t. I would guess that for converted freighters the weight benefit is smaller, as some structural features cannot be removed (doors, for example).

Anyways, as I happen to know the actual OEW of the in service A380, I know there is quite a gap between published values and actual values. I guess for new-built the A380-values (see Wikipedia) may be transferred on other aircraft.
Just the actual given values for OEW are all rubbish.
Officially, the cabin is included in the OEW.
In case of the A380, you’ll find half a dozen of different OEWs.