JonC001,
thank you for this interesting thread!
As far as I can say Blogs as such don't are or form threads. They are sets of articles, each article has meaning by itself (or at least should have) and the article sequence order does not necessarily matter.
When people start to comment on an blog article or entry, their comments form a thread or comment thread. A necessary attribute of threads, comment or otherwise, is that they need a number of entries or postings to make sense, like a real-world discussion.
Forums, by their nature, consist of threads, each containing a discussion between the forum's members.
There! Thank you for your patience!