flatbusher……
I was in both the kosher catering and kosher bakery business in the late 1970s. Most of the wedding and Bar Mitzvah cakes we sold/provided for show were made of styrofoam, cardboard cake circles and hard royal icing.
The actual cakes cut and served were sheet cakes held in the kitchen during the meal. The exception was that the top 6″ tier of a wedding cake was real so that the photographer could get a shot of a bride or groom feeding the spouse a piece of cake (at non-frum but kosher cuisine weddings).