I'm not sure what you call "open", but for me, that means:
- Fully documented (API, SDK, conversion tools)
- Available (optionally with source code)
None of the formats you've linked to in this article meet those criteria. You also missed the top two, most-popular eBook formats out there (in terms of number of readers and number of items available in that format):
- Plucker (with some samples over here)
- iSilo
For non-open, non-free formats though, your blog post is quite informative.