I'm writing from a writer's perspective, not a developer's perspective. Which is not to say that there isn't value to what you're saying, but what I'm looking for is a good way to write quickly, not a code editor that also handles Markdown.
I want to convince the writers I edit on a daily basis to use Markdown because of its clear benefits over WYSIWYG. Sublime Text I'm sure is great and I've heard great things about it, but I'm going to have a far harder time selling the journalists I work with on that than I am with something like Mou or iA Writer.
WordPress' big weakness, IMHO, is that it has an editor which is not built for writing longer pieces and is poorly suited for editing. (Tumblr's big weakness is that it supports Markdown, but without frills.) That in my opinion is a huge issue—the words are basically the most important part of the editing process, and it means that in editing environments we're still stuck using Word or third-party tools like Editorially. What I see with Ghost is a real honest-to-God effort to focus on the editing tools first. We need more of that. It's where we spend most of our time on our blogging platforms. Why downplay that and instead put all of our energy into these inefficient WYSIWYG ContentEditable editors that nobody really, truly likes?
Not everyone who reads HN is a developer.