XSL Titlepage are Pagetitles?

||*()*|| docbook-apps..
      
    While I'm studying DocBook XSL processing mechanizm I've learned,
that generally output page consists of five parts:
    - html header (with html header title);
    - hav header;
    - page header; (or titlepage in templates)
    - main content;
    - nav footer.
    Well, I've got the only question about page header, which is called
"titlepage" in templates. For example refentry template calls
refentry.titlepage to put additional content into div with class
"titlepage" in output html. Am I right?

The question is - Why to render this subdivision to class "titlepage"
when it doesn't produce any page, than can be called "title page" and
used only for rendering page header or "page title"?

-- 
.techtonik