Chanelgirl
As far as I know, chocolate can be used. Even sponge cake can be used, those high density sponge cake but usually used for top tier. Usually with such softer cake, Dowels is a must to prevent each tier from sinking into the one underneath. The other reason for using fruit and buttercake is becos the cake need not be refrigerated immediately. Cos fondant cake will 'sweat' or melt once taken out from the fridge.. so normally ppl would like to use cake base that can be stored in room temperature for about one or two days.