It's also an 'American thing'.
A quick look through a major EASA airline's manuals reveals that Los Angeles LAX, Chicago ORD and New York JFK do not allow Cat3B No DH, whereas they do allow Cat3B with a DH.
However, Denver DEN does allow it!
Not sure where you looked, but I just looked at the CAT II/III plated for LAX and ORD, and none of them had a DH associated with any of the CAT III approaches.