When a fake cake is used for the main wedding cake, what do the bride and groom usually cut during the cake cutting?

You can add one tier a proper cake and then the bride and groom cut it.

One charges the same for a 'fake cake' the same as you would a 'real cake.' Problem solved.
It costs more to buy styrofoam. It costs the same to ice & decorate styrofoam; takes as much work, sweat & tears. So where is the savings??