I wrote some blogging tools way back in Mathematica V 5 which I used for a while. But I haven't revisited the process since then. It's in a set of tools that I wrote for myself (and still use for the general organization of my work in Mathematica). I think a lot can be done to create a new approach if one wanted to--but getting things right is subtle to reproduce all that one can do in a notebook, so taking an approach (if one forgoes the HTMLSave route) where some rules are set that restrict what one can put into a notebook that will be exported is the best starting point, rather than trying to get all the bells and whistles working. Paul-Jean Letourneau's tools are a good start. Internally it seems that Wolfram Research apparently uses a complex workflow (perhaps a WRI employee can comment) to create their blog postings.
But here is what I did about 10 years ago:
The set of tools (I give it away for free these days if anyone's interested... no support though anymore):
http://scientificarts.com/worklife/
Documentation on the blogging functionality:
http://scientificarts.com/worklife/documentation/blogging.html
Some (old marketing) examples of blog postings:
http://scientificarts.com/worklife/wlfwblog/index.html
If I were to do this again I'd certainly take the route to implement it (at least as an option) some form of Markdown along with things like TeX/MathJax, etc...
P.S. All this stuff in this set of tools still works 10 years later with only minimal updates to the code. An amazing testament to the backward compatibility of the Wolfram Language, given that the codebase for this is about 50,000 lines... !
