A tag would denote something as a recipe, a movie review, a book title, a product description, a grade, a headline, a bowling score, etc. Imagine all the things that go into a newspaper. Properly tagged, you could apply a layout engine, using a set of layout rules, to layout an entire newspaper automatically. Not surprisingly, this kind of application is exactly where SGML, the grandfather of HTML, came from. Layout is presentation.
Presentation is layout.
Apply one set of layout rules and get The New York Times . Apply another set and get The Village Voice. I'm talking about layout. I'm writing this document in Microsoft Word. To tell you that The New York Times is a newspaper title, I've used the italic feature, as any good editor would.