Ask HN: Medium charges $75 for pointing the blog to my existing domain?

I was under the impression that Medium lets you point to a custom domain if you already own the domain. But I contacted support and they say that a one time $75 payment is mandatory.

Same goes for Wordpress. They charge $99 per year even if you own a domain. Is this something common? I have talked to people who say they use these features for free, as the domain is already owned. Any ideas?