No matter how much a cake decorator wants to make/sell gumpaste flowers, many brides only want fresh flowers. I have found that most of the time that it's not about the price, but the a overall look. Fresh flowers are just soften the entire look of the cake.
The logistics of fresh flowers on wedding cakes can be tricky. A wedding cake should not be at a wedding too early. If the venue is air conditioned, I recommend not delivering a cake earlier than two hours before the reception. Most often, the florist has already completed their set up by the time you arrive with the cake. That leaves you at the mercy of the florist. Did they leave you enough flowers? Are they the right kind that the bride wanted? Do you know how to arrange them? These are all very real world problems that I have experienced MANY times. In fact, I had a bad feeling once this year and gathered flowers and herbs and brought them with me. I had plenty for the grooms cake but the bride completely forgot the succulents for her wedding cake and they were the entire decoration on the cake! They were giving mint julip cups with succulent cuttings as wedding favors. With permission, we had to take a few apart and wash them really well just to get something on the cake. Honestly, it was not how I wanted to leave the cake, but that's all we could do. I should have trusted my spidey senses and brought some succulents too!