That works for you and me (we're using jekyll here) but not for people that want timed releases and an online editor. Comments will need some sort of database as well, so you'll have to rely on disqus or similar if you're running a static blog.
Comments (outside of Disqus), timed-releases and online editor. Interesting. I can see that.
The blog itself I don't need to be served by the Node app, Apache or Nginx can do that fine.
Well, scheduling and static generation require a cron job that writes the static asset at the predefined time. It all gets complicated from here. You can write the static asset when it's first accessed for example and from there on serve the static file, but that requires a database/storage as well, so you're basically back to square one.
I'd not restrict myself to sqlite here either, but that's a minor nitpick.
I do suspect that Xylakant may be right elsewhere in this thread when she points out that it's not possible on Heroku, but I'm not sure.
Anyway, I would love to see Ghost use a pile of static Markdown files rather than a database for posts. Then, in a couple of years, when I want to use something else, I can take my pile of Markdown files and move along.