Given that we're looking at a free service I would presume that the technologies used by Blogger are probably open source. Based on look, feel and behavior I'd presume that this would take the form of a close cousin to the LAMP framework but maybe with some proprietaty middleware in place of Perl/PHP.

Based on my analysis I surmise that the following steps take place when I save a new post. These are of course expressed in layman's terms since I don't know the actual technologies in use.
1) My browser sends a request to the web server to update a database with the contents of my posting.
2) The web server delivers the request to whatever middleware is in use.
3) The database stores the new post, probably with the "blogID" value as the primary key.
4) The database stores only the contents of the post, not the template. I'd expect that the template is stored separately for a variety of reasons, not the least of them being to reduce the size of the database. Also, changes to the template affect past postings as well as new ones, which indicates that the template is completely separate from the data.
5) This is my first post in a while but I presume that the database, middleware, web server and ultimately my browser will present me with some sort of confirmation message.
6) My browser requests the page containing my new post.
7) The web server sends the request for data to the middleware.
8) The middleware delivers this request to the database and the query results are returned.
9) The middleware delivers the results of the query to the web server.
10) The web server locates the appropriate template and renders the data into a web page based on that template.
11) My browser displays the resulting web page.