And yet, it contributed to what is considered to be a very successful product. It's not that learning how to do calligraphy made the product work, its knowing about calligraphy and being exposed to it.
How do you differentiate a product? Some engineers would point to making it perform faster with some sort of better underlying technology. But what happens when everything pretty much works the same way? What if good looking fonts are actually more important than raw speed or even more functionality?
And what use does your app have unless you can communicate its value yourself? There are those who denigrate marketing people, but those very same people need the marketing folks to sell their product because the engineer lacks the capability to communicate the value of the product to others, and may not even want to be involved. Yet, you need those sorts to allow you to be successful because they have a skill set that engineers don't uniformly have.