What is namely the service? Too provide a cake? Or to provide a "wedding cake" ? I think there is a distinction. In the second case the question naturally presents itself, "What is a wedding?"
My whole point in this is that if you provide wedding cakes to heterosexuals [with inscriptions - thus, being "custom"], then you can't refuse a same-sex wedding cake. As long as the inscription isn't obscene or otherwise violate law.
The article does not say that they make traditional wedding cakes - but dollars to donutz, they do ...