Pie trumps cake simply because people get hit in the face with them.
You haven't been to any weddings, have you? There's a bit where the groom is supposed to feed the bride a piece of the wedding cake, and 'traditionally', it ends up all over her face. (We had an ice cream cake, which soundly confused that issue. Not to mention the 'tradition' of single guests putting a piece under their pillow to dream of their spouse-to-be.)