While I believe small size of blog posts is one of the reasons why blogging is so popular, lack of structure in blog posts limits the range of blogging application.

Typical blog posts are textual and unstructured except for hyperlinks, light presentation markups (i.e. bold, italic), and enumerations (ordered and unordered lists) plus optional title.  They are like smaller versions of web pages which leaves little room for automation and reuse.