The subscription system, as I mentioned upthread. Making a blog is easy. Making a blog with pay gated access to posts and downloads is not. The closest equivalent is Patreon + WordPress with the Patreon plugin. I already mentioned the issue with self-hosted WordPress. Managed solutions cost more than Ghost and provide less.
Yep. I don't mind Ghost or Automattic charging so much for managed hosting. That also pays for development. I don't want to assume other managed hosts charging more for WordPress without doing anything more is just greed, but it has the look.
That's why I want Ghost to offer a lower tier. That way I could get started at a price I can afford where I'm at, support the development of Ghost, and have an easy upgrade path if I need it. It's the curve, not the price, that I don't like.