Ask HN: ELI5 why I have to learn Machine Learning to use it?

Ok, this could be a stupid question.. But I've seen a lot of people asking how they can learn data science or machine learning, with the majority of answers referring to Andrew Ng's Stanford Coursera course.

With services like Amazon's Machine Learning, why (as a web developer) do I need to learn machine learning? Can I learn the basics and just let the services do the work for me?